I recently started getting a hard thump when boosting my car. It's not traction control, or clutch. Feels like a differential problem.

 

maybe boost cut?

 

Sounds like drivetrain noise to me. The nose of the rear diff can bump the underside of the car when the mounts go south. Common issue on the b5's.

 

if the car is over boosting and cutting boost, shouldn't I be throwing a CEL (Check engine light) or a code? no CEL's or codes are coming up. this is a random "thump" im experiencing under acceleration, seems to happen in the later gears under load. ( 3rd thru 6th). because its not happening every pull, could I be dealing with some type of mount that's failing like a diff mount that is could be causing the thump? Thanks for the help

 

are there any threads on this if its a common issue? thanks for the reply~!

I may have posted in the wrong sub forum,

my car is a late model B5 S4 Avant with 237k miles on the clock. thanks guys

 

You should inspect all bushings, bearings and mounts under the car.

Your search will become a lot slimmer.

 

trani mounts or nose cone mount on the front of the diff