It could be a suspension part such as a control arm. I just had replace the rear control arms on my 1993 Toyota Celica because the bearings in the control arms were worn out. It made a lot of rattling and thumping; when I replaced the arms the sound stopped.
Could be a bad ball joint
I have a 99 A6 quattro and have changed the brakes out on it multiple times. email me if you need to know anything. Doster@marshall.edu
The tire itself may be bad, with a flat spot (no tread) or bulge. Also, a wheel that is badly out of balance can thump at some speeds.
use a vag com or just unplug and replug
How much freon does 99 Tahoe with rear ac hold
no.
replace rear brake hydrolics
in the rear
rear seats
i don't know if it helps, but my '99 legacy outback was making a knocking sound. turned out that the oring on the brake caliper pin had worn out, and the pin was kind of knocking around.
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