My '99 V6 30V w/ 59K miles has started to make a strange noise.
It is quiet until warmed up, then the sound starts. I suspect something emmisions-wise is activating after warmup.
It sounds like a rattle, or gulping, abouty 2-3 hz, fluid or air I can't decide. It does increase w/ throttle, but not proportionally - it just speeds up a bit. volume is pretty steady, it doesn't get louder.
So, I don't think it's in the valve train. Perhaps intake? Is there something that might be "flapping" in there, some sort of proportioning valve? (mine is NOT a VR6, it's the 30-valve Audi engine).
I think it's "sucking" realted, if that makes sense. I checked the PCV pipes, a little gunky but clear; no cracks found. The combi-valve is working, tho there was a vacuum leak in its line which has been fixed. The secondary air-injector motor runs normally - the sounds isn't realted to it running.
I've looked all over, it is not something vibrating nearby in the engine compartment.
The engine runs fine otherwise, but I suspect something is on the way out.
I don't think it's water pump either, since the noise isn't tied to engine rpm. But hell, I just don't know, that's why I'm, asking!