Noise & Warning Light on 2002 TT Quattro

Dear Forum Members,

I have a 2002 TT Quattro Convertible with 80k miles.

Yellow warning Triangle light came on at the same time as some noise in the front undercarriage - lost power for a few minutes - so I thought I lost a belt - but then it drove fine. Brought to a garage - they could not fine a problem, said I'd need full diagnostics.

Warning light (triangle with !) now stays on frequently and flickers - I've heard the rumbling sounds a few times again. Any ideas?

Thanks!
Eric