1997 164 3.0 24v Super Auto

Whenever I start my project car, it sounds like a diesel and then smooths out as it warms up. There are no exhaust blows, so does anyone know what might be wrong ? Could the hydraulic tappets be sticking ?

Any advice gratefully received.

Dave

Yes I think I know,earlier in the year had a 2.5 v6,EXACTLY the
same symptons which went away when warmed up.
Worn Cambelt tensioner/idlers,apparentally the engine expands when
warmed up and the noise goes away.
Had the belts and tensioner changed,ran quiet after that even when
stone cold,this engine does not normally suffer from sticking hydraulic
tappets,it does sound like that I know.