Hey bro,
I have the same symptoms you describe here, but I am almost sure mine is the differential. My car has about 171 000 miles on it.
This are the symptoms I have experienced:
- When I engage the clutch from a stop i get a clunk and a sound like two metal plates are slapped against each other.
- When I let off the gas or get back on the gas at low speeds, I feel the clunk from behind quite strongly with the same sound described above.
- When slowing to a red light from a high gear (gear 3 or 4 for example) and then letting off the brakes to coast (car is at about 1000 to 1300 rpm)
the car kinda feels like its hopping from the rear end with the same sound as I am coasting, until I push the clutch in and put it in neutral.
-At very high speeds (in 5th gear) when I let off or get on the gas I feel only a slight tug with no noise.
I spent half a day trying to diagnose this problem one day. I jacked up the car from the rear wheels with the front wheels stopped from rolling. My friend drove the car (at low speeds of course) while I was underneath listening for the noises and it was most definitely resonating from the differential casing.
People have always told me that its normal but I've never felt this on any other rear wheel drive car (open or LSD). After extensive research I believe that clutch type LSDs like the mk3's require a lot of fluid changes to prevent these clunking problems. I'm going to try replacing my differential with a JDM torsen unit and see if I have the same problem.