Hey guys, need your advice again. I have a 2013 Mustang GT, 6-speed MT-82 with 3.73 gears. I have a loud whine/howl coming from the rear end of the car. It increases with my speed. Below 30mph, it's not noticeable unless you're listening really hard for it. As you get up to 60mph, it gets much louder. Above 60mph, it's very noticeable and very loud. It doesn't matter what gear I am in and the volume of the whine doesn't increase or decrease depending on gear. It only varies (getting louder) with speed. There's no volume change on deceleration. If I take my foot off the gas, the whine almost completely goes away. As soon as I give it any throttle, even 1%, the noise is back with the same loud volume. I'm also hearing a bit of clunking and rattling at certain times on deceleration and just maintaining flow of traffic speeds.

I got the car about 3-4 months ago. I noticed this noise about a month ago and it was fairly quiet and bearable. I could hear it more with windows up as it droned a bit in the cabin. Couldn't hear it with windows down. Yesterday, this noise suddenly got a lot worse and now it's very loud and drones a ton in the cabin. Windows down, it can still be heard. It overpowers my Corsa mufflers and resonator delete.

My 2013 Mustang GT has 3.73 gears from the factory. Stock driveshaft. I have J&M lower control arms, J&M LCA relo brackets, a non-adjustable upper control arm and mount (unknown brand), panhard bar, Koni yellows, and Steeda springs. I've heard the stiffer you make the rear end, the more NVH you have.

I'm thinking it's coming from the driveshaft or differential. I don't believe there's been any work done to the differential previously. I've heard 3.73s are typically whiney but I don't think this is a situation of "it's just a regular noise and it'll be fine" as it got much louder this weekend to the point where the car is annoying to drive. I've heard it could be a lack of diff fluid but I'm doubting it based on the sudden increase in volume and I don't have any leaks in the diff.

Any thoughts as to what it could be and where I should start? Thanks for the help in advance!

you saying it goes away with gas pedal is def the dif

Tonymustang302 said:

you saying it goes away with gas pedal is def the dif

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I believe 80-90% of the sound goes away from coming off of the gas pedal. Not completely but definitely a lot of it.

Since you've bought it, have you taken it to the dragstrip or otherwise performed hard standing start launches?

Coz said:

Since you've bought it, have you taken it to the dragstrip or otherwise performed hard standing start launches?

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Haven't taken it to the drag strip. I've done a few launches and spun the tires, but nothing insane. No really heavy clutch drops, just a few light ones. I'd say a maximum of 5 or 6 light launches since I bought it.

Tonymustang302 said:

you saying it goes away with gas pedal is def the dif

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That's what I was thinking. Sounds like the best option is to take the cover of the rear, pull the axles for inspection and then take out the differential and gears. You should at least get answers to some questions.

Agree with all of the above.

I see you just got the car a few months ago, but what is the current mileage?

Always start off with the easy things 1st.

Plan a maintenance service on the rear Diff & inspect it while you have the cover off. Then proceed depending on what you find.

Check the upper control arm & Diff hsg. Bushing. The UCA can transmit a lot of gear noise.

Check the driveshaft. If OEM it has a center Mount and bearing to inspect.

Good luck & keep us posted.

Ring and pinion gear

Hey guys, thank you for all of the advice on getting the issue fixed! I ended up taking into a differential specialized in shop in Arizona, and they fixed it. I felt the job was over my head as I had never done any work on my differentials before. It ended up being a bad inner pinion bearing. They said the gears and all other bearings looked great, just the inner pinion bearing was bad. Had to remove the center bearings to get to it. After they replaced that, the car dramatically decreased in NVH from the diff.

But it hasn't completely gone away. As of now, at 60MPH and above, I do still get a small whine. Absolutely no whine or howl below 60MPH. I assume that is just the 3.73 gears whining since they tend to be loud. The car has been fixed for about 5 days now, and the whine has gotten a small amount louder than the day I fixed it, but nothing close to how loud it was pre-bearing fix. Contemplating adding more Ford friction modifier to see if that helps.

Once again, thank you for all the advice on the issue! Glad I got it fixed and I'm able to have fun with the car once again.

302 Hi Pro said:

Agree with all of the above.

I see you just got the car a few months ago, but what is the current mileage?

Always start off with the easy things 1st.

Plan a maintenance service on the rear Diff & inspect it while you have the cover off. Then proceed depending on what you find.

Check the upper control arm & Diff hsg. Bushing. The UCA can transmit a lot of gear noise.

Check the driveshaft. If OEM it has a center Mount and bearing to inspect.

Good luck & keep us posted.

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The car currently has 103,xxx miles on it. The trans and engine have about 70k miles on them since they were replaced by Ford early in this car's life. I do have a UCA and UCA mount installed, but it was installed from the 1st owner (I'm the 3rd owner) and I don't know the brand nor is it adjustable. I'm likely going to check the pinion angle and if it is off, I'll buy an adjustable UCA. Maybe that is some of the cause of the current low volume whine noise above 60MPH. Thanks for your input on all of this!

With 100,000 plus miles on the clock, check the rubber bushing at the top of the Differential housing while you’re there.

Keep in mind that aftermarket UCA's on the rear will also transmit more NVH than a stock one. My car (T-56 magnum XL swapped 2012) has 4.10s, and when I switched to an aftermarket UCA with BMR bushings to correct the pinion angle I hear a lot more gear whine in the cabin than I did before. It did fix a slight vibration from the pinion angle being out 4 degrees though.

+1 to 302 Hi Pro's suggestion to inspect that bushing. Could be worth bringing it to the same shop to have them replace it with another stock one since it's kind of a PITA to change with the rear still in the car.

Just my two cents worth, but once a ring and pinion gear set has been run with a bad bearing the mating pattern of the gears is messed up and putting new bearings in may quiet it some but your not going to get a quiet running rear end back. The ring and pinion gear interface is very sensitive to minor changes. It also doesn't help that most differentials are a pain to set up, that's why a Ford 9" is a popular diff, much easier to dial it in.

pjs57 said:

Keep in mind that aftermarket UCA's on the rear will also transmit more NVH than a stock one. My car (T-56 magnum XL swapped 2012) has 4.10s, and when I switched to an aftermarket UCA with BMR bushings to correct the pinion angle I hear a lot more gear whine in the cabin than I did before. It did fix a slight vibration from the pinion angle being out 4 degrees though.

+1 to 302 Hi Pro's suggestion to inspect that bushing. Could be worth bringing it to the same shop to have them replace it with another stock one since it's kind of a PITA to change with the rear still in the car.

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I'll definitely have to check out that rubber bushing then. I assume there's no way to check the bushing without taking it out. Problem is, that shop is quite far from me. But I'll definitely look into doing that if the noise is getting bad to the point where it needs to be looked at again. Right now, it's tolerable and is only really noticeable at 60-65mph. I know I have an aftermarket UCA in there right now, but it could be a shitty brand. So I'll probably look into something adjustable from BMR or Whiteline.

xr7 said:

Just my two cents worth, but once a ring and pinion gear set has been run with a bad bearing the mating pattern of the gears is messed up and putting new bearings in may quiet it some but your not going to get a quiet running rear end back. The ring and pinion gear interface is very sensitive to minor changes. It also doesn't help that most differentials are a pain to set up, that's why a Ford 9" is a popular diff, much easier to dial it in.

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Ah, that makes a lot of sense. I didn't know it was that sensitive. For a shop that has done rear gears for 12 years, I would have expected them to tell me something important like that. Oh well, the noise is completely tolerable for now. Hoping it doesn't get much louder and I don't have to bring it back for a full ring and pinion and bearing replacement.

Its polyurethane lca's transmitting harmonic vibrations that were always there. 3.73 are know to whine. I had whiteline lca's and had the same exact noise. I went back to track pack lca and oem uca

Coz said:

Since you've bought it, have you taken it to the dragstrip or otherwise performed hard standing start launches?

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I know this is a pretty old thread, but I’m have a very similar situation.

Would there be a specific reason you asked about the hard launches?

My story differs a bit:
2012 boss 302 with 10k miles. 2nd owner, bought 2 years ago with 7500 mi. WAS all stock and went to the drag strip and experienced what I’d call pretty significant wheel hop. Had been thinking of lowering and control arms so this sent me to do it. Boss 302 lowering springs and BMR poly panhard bar, UCA and LCA. Instantly experienced a loud howl from the rear basically as explained in the OP. Went to differential shop in Springfield, MO and he replaced the ring and pinion with ford parts. No change. He warrantied the work and put a 3rd set in. Still not much of a change. After this all happened driving down the highway I get a low humming above 70 which turns in to a warble above 80. This may or may not have been there prior to the ring and pinion change but I sure didn’t notice it.

So my questions are, would wheel hop potentially cause others issues that might result in the low tone rumble/warbke, like damage to bearings that wouldn’t have been replaced with the R and P? Driveshaft damage? Or any other thoughts why 2 new sets of gears are still really loud?

Thanks for any thoughts anyone might be willing to share!

Did you fit the BMR upper control arm?

I did set it to the stock length for install and then had a shop adjust the pinion angle. They said it was -3 and took it to -2.

I did set it to the stock length for install and then had a shop adjust the pinion angle. They said it was -3 and took it to -2.