Humming Noise & Low Frequency Vibration

[geneva]

I have a humming noise and very minor vibration that comes and goes at speeds of @ 40, 60, and most pronounce @ 73 mph. Also continues to come and go at higher speeds as well. I had an electronic vibration analysis preformed which picked up the vibration @ 108 Hz. and but could not pin point where it's coming from. Sounds like coming from the front but hard to confirm. New PSS recently installed and load balanced. Wheel bearings inspected with no issues. Noise is there with/without car in gear or coasting in neutral. I have a DSS one piece alum. drive shaft installed but noise was there prior to install. My thought is rear diff. as I blew a right rear axle seal during a track day and leaked a fair amount of fluid. But humming noise doesn't sound like is coming from the rear and vibration I can feel in the floorboard but very minor almost more like a tingling. I'm out of ideas and my local Ford dealer has also not been able to track it down. I've now run three track days with this issue and at some point I'm afraid of some type of failure. Any ideas????

 

[cosm3os]

How about clutch in v. clutch engaged? If it happens with both and you are sure the bearings are good (as much tracking as you do, I'd be suspect), it has to be the tires. Try moving them around and see if it moves or goes away.

 

[kcbrown]

Does the frequency vary with speed? With engine RPM? You should be able to disambiguate between the two by going the same speed but in different gears.

 

[WinterSucks]

I am also suspicious since you are listing three speeds which look like they could be at the same rpm in 4th, 5th, and then 6th.

 

[geneva]

thanks for all the input and I was able to finally track down the humming/vib. to a left front caliper hanging up. With tracking the car so much and running race spec pads (Padgid RS 29) there was a high amount of brake dust build up that was causing the problem. Once I dissasembled, thoroughly cleaned, and lubed the knock out pins the problem went away. Upon further inspection I also noticed an issue with the other caliper as the brake pad retaining clip had twisted to one side. I'm sure as a result of all the heat & torque generated under heavy threshold braking. A proper cleaning will now be included as part of my maintaince routine after every track day.

 

[F.D. Sako]

I had the same issue of the metal spring rotating as well. I didn't notice any humming, but I knocked it in place between sessions.