Rear diff whine after track sessions (Dark Horse) – normal?

[EricH]

I’ve started doing more track days and I’ve noticed something consistent after sessions:

• After coming off track, I hear a continuous whirring/whining noise from the rear of the car. No vibration, no grinding, just a clean whine that goes away with heat.
• It’s most noticeable at low speeds rolling through the paddock
• Sounds almost like a gear or electric motor whine
• It fades away after a few minutes once things cool down
• I don’t hear it during normal street driving
• Has never gone into 'limp' mode, and no dash/engine lights/faults

Car is otherwise stock, curious if this is:

• Normal diff heat / fluid behavior on track
• Something others have experienced with these cars
• Or an early sign I should be looking at fluid / maintenance / cooling

Would also be helpful to know:

• How often you guys are changing diff fluid with regular track use
• If anyone has upgraded fluid or added cooling and noticed a difference

This is first mustang I've ever owned- Appreciate any insight, just trying to stay ahead of anything before it becomes a bigger issue.

 

[67GTA]

Does your Dark Horse have the Handling Package? I’m guessing it does and you’re hearing the electric pump for the differential cooling system.