Had this noise for a while louder when cold softens up when warm had a good prod around with long screwdriver seems to be loudest on no1 cylinder head bolt the one closest to the front IP (edc) side .changed the cylinder head (unrelated job) due to multiple cracks and the noise stopped the engine sounded fantastic for 200 miles but now it's back and a bit stumped where to go with this not sure if cylinder head has failed no sign of gasket failure rechecked valve clearances all ok there.to me it sounds like mild piston slap but checked cylinder bores no sign of uneven wear and the spiral Finnish on wall looked fine and even over all cylinders any ideas as it drives great but sounds like a bag of doo doo.