ticking noise on slowing down

checked the tappits ..all fine, engine had new shells, and checked gudgeon pins..new rings etc...at 78000 (now 100000)

when i take my foot off the throttle at 50-30mph you hear a ticking noise similar to a stone in a tyre...have been advised to check fuel lift pump arm, and vacuum pump...brakes servo fine. Have put 2 new injectors in (recon) will put the other 2 in next week

any other ideas ?

Shine a bright torch behind the head near the bulkhead and start it up !look for smoke from head at the back !! Gasket can blow to atmosphere and sounds like a tapping noise !! Usualy still run fine and don't loose any water or oil !!
Worth a try !!