Well my wife and I just purchased a 2002 Jetta 4 cylinder turbo yesterday. I gotta say...this is one NICE car. A couple things concern us though. One thing I have never heard from a car is a loud "thunk" sound when travelling at high speed and applying the break quickly. Ive discovered that it is in fact the rear breaks hitting the rotors really fast. I checked the manual and it states that it has some sort of break booster feature and I thought that it might do that normally but I cannot be sure. The other sound is almost exactly like the breaks "thunk" sound but sounds more like it comes from the drivers side and happens when we hit bumps at high speed. Driving down the freeway and hitting a bump causes a "thunk" sound that is almost identical to the other one the breaks make. It comes from the rear of the car and this is a front wheel drive car but...the manual said there is something called EDI that is supposed to help balance the car in slippery situations and it stated that it might make noises when it engages. I really know nothing about these cars. This is high end for me...im a Jeeper. Any information that could help me with this problem would be greatly appreciated. Also...the suspension seems fine and I checked the exhaust and it doesnt seem to moving around too much.

 

Just a guess, high speed and hitting the brakes quickly
can activate the ABS brake system and that will make
a noise. The sound when hitting the bumps, the car has
4 wheel independent suspension, McPherson struts, they
are bad about making clunk or thunk noise when they get
a little wear, and will cost your a** a bunch to replace,
and only last about 1 year and start the noise again.