My '99 TDi 115 estate has started making an absolutely terrible noise.

Its a rumbling, scraping, knocking type noise that seems to be coming from the front of the engine bay. Its clearly audible from inside the car and out. Its constant but rises and falls with the engine speed, although I don't think its coming from within the block or cylinder head.

The engine and transmission / clutch are (currently) performing normally, as are the ancillaries (alternator, water pump, etc.)

It started quite suddenly and is definitely getting worse.

Other than that, all I can say is that its very loud and sounds expensive

Anyone know what it might be?

Regards, Desperate noobie

P.S. I ran low on oil a couple of weeks back, just until the warning light came on, but I filled it up straight away so I wouldn't have thought this would be related........