Very light thumping (like a sewing machine) (2013 GTS 70k miles)

[GooseRonalds]

Hey all - I've got a 2013 Cayenne GTS with 70,000 miles on it. About 10k miles ago, I noticed what felt like the TC failing (bad shifts, slipping on turns, chop in the driveline) and did the Ravenol swap twice and it entirely disappeared. At the same time, I did both differential fluids just cause. Just now I am noticing a very slight "thump" in the driveline that is commensurate with speed, and not engine RPM. If I am cruising and throw it into neutral - the noise entirely disappears, so I'm ruling out things that are always in motion and could only be things hooked to the driveline. It's not the "midget with a hammer" noise the previous gens had with the driveshaft center support - it's much more subtle. So, what moves only when it's in drive? Any ideas? Front diff? TC finally letting go? Thanks!

[av8sky]

I am going to guess your driveshaft is going bad. Technically it is the bearing support that goes bad on these. The only real fix is a new driveshaft. Have a look underneath. I would also research bad drive shaft on a 958  as well. To see if my guess is correct.

[GooseRonalds]

Hmmmm. So, I haven't gone under there to shake things around to see if there is any slop - assume that is how you would diagnose this, right? Was planning on doing that this weekend when I get some time to get under there. I looked into that, but it's hard to find any examples of it starting to fail - all the examples sound like a complete failure where the driveshaft is bouncing around, sounding like someone is hammering under your arm rest. If it is that, any thoughts on the EPS mounting support? People seem to have success with that bad boy.

[av8sky]

I have never experienced this personally. I would guess shaking the driveshaft near the bearing support. As far as the EPS mount support goes I have no experience with that either.

[GooseRonalds]

I just drove it up on a couple 2x6 with the air suspension raised and locked out, parking brake on, transmission in neutral. I was pulling on it pretty good on both sides of the support and there was almost no movement at all. Maybe a fraction of a millimeter, but well within what I would consider tolerance. It's not noticeable until about 10 mph. From outside the car is sounds like a dust shield rubbing on a warped caliper. Very soft metal on metal noise that changes frequency based on your speed. 

[GooseRonalds]

Just heard back from the shop - it's the front differential and it's not cheap.