300tdi engine chuffing noise

Hi guys I am Simon I'm new here had a look around some threads on here but I'm still having abit of a problem I bought another discovery 1 after rebuilding a 200tdi from scrap but now I'm on to this 300 tdi but I can't seem to find the chuffing / kinda tapping noise I have changed manifold gasket as I thought it was there but nope still making the noise put my hand round the back of the block couldn't feel anything there I'm kinda running out of ideas I got a feeling it is the head gasket but I don't won't to start ripping it apart

I had similar a few years back, turned out to be a loose/lost (can't remember) manifold stud, the closest to the bulkhead!

manifold gasket ,head gasket or valve stem cap is common with chuffing or other reason valve not opening fully

chuffing hell that aint good

Haha thanks guys I changed the manifold gasket n it's still doing I'm guessing it will be just keep checking diffrent parts till I find it now I got **** load of welding to do anyway so il get all that done before stripping the front down haha but thanks for the reply