Low drone/hum noise at 1700RPM?
I have been getting this humming noise coming from the car when the revs hit between 1600 - 1800 RPM (almost exactly 1700). I don't get it if the car is out off gear and I rev it up as I've tried it's only when in gear and driving. It's sounds like a deep drone or hum and only lasts a few seconds whilst between those rpms but as those rpms are regular revs to be in I get it quite often. Whilst not overly loud it is loud enough to catch my attention.
Tried all kinds of searches over the past few months but can't seem to find anyone else with a similiar problem. Anyone here have any idea what it could be? If I was to guess I've always thought it was the CAT Converter but that is only a guess.
It's a B5 1.9 TDI SE
Not sure I have explained it the best here so if anyone needs any further information just ask. It's hard to describe a noise.
Thanks in advance