I just changed the headgasket on my 95 ls. replaced valve stem seals, cleaned everything, reseated valves, got everything back together and its making a horrible clanking noise. it is rhythmical, but i cant tell where its coming from. can some people please give some ideas of what it could be? ... i dont think its in the belts although i havent taken them all apart. and last think... when i run higher rpm the noise goes away.

will appreciate any ideas as soon as possible, thanks