Please help me identify this sound

#1

At VIR this weekend, in the middle of Sunday qualifying, I noticed a new and very rhythmic chuffing kind of sound. I finished the session and on the cool-down lap, I dropped the engine to idle/trans in neutral, and the sound became much easier to hear. This sound did not build up over time; it went from I never heard it before to I heard it very clearly even while under power (even though that’s not apparent from the clip)

Please ignore the first odd sound on the clip; I have that all the time and guess it may be my camera mount moving around. Wait for the parts where the motor is at idle, most noticeable at:
1:12 - 1:25
1:40 - 1:50
0:34 - 0:48 (less obvious)

I have a theory but would like to hear other opinions. Vimeo still in post-processing but should be up by 11:30pm Eastern.

https://vimeo.com/46266191

Thanks in advance for any helpful suggestions. This damn sound caused me to abandon the Sunday race, leaving me with only 1 green-flag race lap for the entire weekend. Bummed doesn’t begin to describe it.

#2

It kind of sounds like loose lug nuts, loose drive shaft and or center support. What have you checked so far?

#3

I checked the wheel nuts and they were tight. Jacked up the rear end and ran it in gear for a bit. A friend who was there that runs a repair business, based on my description of the frequency of the sound, convinced me it was something traveling at ‘wheel speed’, not ‘driveshaft speed’, so we were looking hard at the rear axles.

However, I wasn’t smart enough at the time to pull this clip and play it for him!

Although we didn’t hear anything, the LR axle seemed to be doing a bit of the “hokey pokey” in-and-out, up-and-down, so suspected a failed joint.

I did not look at the driveshaft at all, but I will.

#4

I agree with BTM that it sounds like a loose wheel but you have eliminated that.

Rear wheel bearing maybe?

#5

I vote - center support bearing,maybe pinion bearing. Sounds to be at a frequency that is faster than wheel speed…