please could somebody tell me the reason i got a noise of a belt hiting the cover somtimes on my fiat doblo and wot will happen if i leave it .thanks

Cover of what, FCS?

If it's a loose cam belt, the result of leaving it on a 16v engines or on a deisel, will be a new engine.

If it's an 8v FIRE engine, you'll just be stuck in the middle lane of the M62 with a Hungarian who has not slept for 2 days approaching you in an artic at 68mph.