Vaux did my cambelt last week (Z20LET) and now when cold + at very low revs, there is a slight 'tap tap' noise. Its only when u put your foot on accelerator and as soon as it reaches 2000rpm it stops.

Any ideas? When i asked the technician what had to be done, he said an engine mount needed to be removed and one side of the engine jacked up to gain access to fit the new belt. Maybe they forgot to tighten something back up?