Small update:
I was prepping the car for another track day and knew that I needed to swap to my spare TII axles (passenger side inner CV was in poor shape). I assumed that this was the cause of a rhythmic thump that becomes significant under light load.When coasting at any speed it does not make much of a noise. To investigate this, I detached both axles from the diff and ran the car through the gears on a hoist. The vibration was non existent inside of the car and a colleague was unable to detect it with his ears or stethoscope from underneath.
After swapping to my spare axles, the noise was reduced but is still present. It sounds and feels like it is localized to the end of the trans/start of driveshaft at this point.
I'm going to investigate further as soon as I get a chance, but I thought I should mention it to see if anybody else has experienced a similar issue.
Notes:
- Adapter from trans output flange to driveshaft is concentric, adequately fastened and statically balanced
- U joints in the driveshaft are 1350 series and all in good shape
- Driveshaft angle is very similar to what I have used since 2009 in a variety of engine swaps to the TII diff in an FC
- Driveshaft was dynamically balanced and the weights have not come off
- This issue was not present until the last track day.
