V6 Vibration at 1800-1900rpm

[Waynester2]

Hi Guys,
This is not a A8 question, but I figured there are some clever chaps in here that might have come across this. I have just bought an A4 B6 (2004)
My engine (2.4 V6) has a vibration at around 1800rpm.As soon as the rev counter goes past 2000, it smooths out again. It's only at that crank speed, the rest of the time it's smooth as silk. My local garage reckoned it might be the dual-mass flywheel.
I don't think it's gearbox related, because if I rev it to 1800rpm in neutral, while stationary it still does it. (clutch in or out) I've no idea what is causing it, my local indi said it might be the dual mass flywheel, which this engine does have, but has said to replace it will cost over £1k with no garantee of a fix, which is a bit risky. He has also said it could be the crank shaft pulley which is a lot cheaper.

Anyone ever seen this? Otherwise it runs fine, car has only done 42k mpg is good for the engine, tickover a bit lumpy but not the worse I have seen.

Any suggestions very welcome.

Thanks

Wayne