2001 A3 TDI 110. Noticed this morning it started to make a weird noise i've not heard before. Best way to describe it is a electrical car sound or sounds like a supercharger(Not quite but you get what i mean) and vibrates, generally between 1.5k-2.5k rpm, does in both neutral and gear so know it isn't gearbox. From what i've gathered it may be the cat or engine cover? Any ideas?