EDIT: FOUND THE CULPRIT! Description in the end.
This may be a long post, but my car is making a sound that is driving me completely nuts. The car in question is a 1997 VW Parati, a small three-door wagon sold in Brazil and Latin America.
The sound can be best described as a metallic clunking, a 'tac tac tac tac' that the car makes when I am accelerating. The noise takes a while to begin, after the first drive of the day, probably because the faulty part needs to heat up (and expand) before getting loose and start rattling. The frequency of the 'tac tac's matches the speed: On low speed they're well spaced away, but on high speeds it's intermittent, and very fast.
But, independent of the speed I'm going, whenever I depress the clutch and coast, the noise immediately stops. For example, if I'm going at 80 km/h and the noise is very fast, I depress the clutch and it stops immediately. Once I get the car back in gear, it resumes.
The sound appears to be coming from the front right wheel. The funny part about it is that my mechanic looked everything, but couldn't find anything loose or broken. Worse still, he fastened the screws and bolts underneath and the car stopped making the noise for some 3k or 4k km.
Now for symptoms, or the lack of them altogether: The steering is tight (I don't really know the term in English for this, but I mean that it isn't loose), the car has no tendency of going left or right by itself, I don't feel vibrations on the clutch pedal or the gear lever and the car revs and accelerates normally.
It seems, for me, that this is related to the clutch somehow. However, this doesn't explains why, in the other time, my mechanic just tightened the bolts underneath and the noise stopped for months. He thinks there's a heat shield loose, and he noticed that my front shock coils are going bad, but neither the shields nor this don't explains why the noise pops just when I'm accelerating.
The noise indeed is worse when I floor the throttle, or when the engine is forced on a hill.
On his inspection, the CV joints looked good, and he found nothing really loose underneath the car.
So, what do you think about it? Can I have a bad CV axle or joint? Or maybe it's time to open the clutch to check? Opening the clutch is the last thing I want to do, because this would be very expensive, so I'm trying to isolate the problem before resorting to checking the clutch.
Thanks in advance!
EDIT: My mechanic and I found out what was making the noise. The inner CV joint was worn out, and the grease has dried completely. With a new joint the car is now smooth as butter :-)