Crunching / grinding sound

[Aaron1989]

Hi, I apologise if this has been discussed previously but I can't find any info on this, so any responses I would really appreciate.

I started my 56 plate 2.0 tdi yesterday morning and there was this horrible crunching/grinding sound coming from the engine bay. It lasted 10-15 seconds and stopped. Later that day I started it 2-3 more times and nothing. Then again this morning the same, it seems to stop when revving but returns when idling, and again it lasted approx 15 seconds.

Does anyone know what this could be?

Thanks in advance

Aaron