tapping from top of engine

Hi
Just had head gasket replaced (1.8 petrol) and every now and then on starting there is a single loud tapping coming from the engine. It goes eventually after a few mins and does not occur every time. Did it before i had head gasket changed but very faint and went after a few seconds. Searched threads and said small end? Cant see that as noise would get worse as the engine got hotter? Are the tappets hydraulic and if so could the engine oil cause this problem. I always filled with castrol magnetec and know the garage changed the oil but not what they put in?
Butty

lifters
a flushing oil and DO NOT drive it- drain oil and new oil and filter

Hydraulic lifters are like hydraulic jacks that maintain valve clearances, they have small oil feed holes that easily block.
Hopefully you kept them ordered so the wear is matched

Cheers for that will do it this week. I hope the garage kept them in the same order. If they aint could this cause the problem and would the engine have to be stripped down?
Butty

Hopefully they were kept in order-try flushing oil first and then post back how you get on.

Get engine hot, pour in flushing oil and run engine as recommended (below 2000 rpm normally for the time suggested-DO NOT DRIVE)

Stop engine and drain oil thoroughly and replace oil and filter.
Hopefully cruddy oil from head gasket failure is the cause of it and flushing oil will cure it

Top tip
Cured the prob. No more tapping!
Butty