[Vwdiesel] 02 TDI, faint tapping when under load

[Stephen Sherman]

My new to me 02 Jetta TDI has a faint tapping noise which has me 
concerned. I've had a few people listen to it, and opinions vary, some 
thinking it is in the dash, others (including me) thinking it is coming 
from the engine or drivetrain.

Symptoms are that when the engine is under load, accelerating or going 
up hill, there is a faint tap, tap tap noise.  If you let up on the go 
pedal, the tapping stops immediately (so it doesn't seem like it could 
be wheel/tire related), and resumes as soon as you push on the pedal 
again.  It does not tap if you just have it in neutral and rev the 
engine, no load.  The frequency of the tapping varies a bit but is 
generally in the 5-10 taps per second range (just rough counting here). 
I've tried to notice if it changes frequency around gear shifts (auto 
tranny) but have not gotten anything conclusive.

I have tried listening with a mechanics stethoscope, but did not hear 
anything that seem to be it (again doesn't tap when not under load. I 
have checked the CV joints, and no obvious play in any of them.

Any other things to check out? Ideas on what it might be?

TIA