i have a 2004 g35x. recently replaced the spark plugs and changed oil. after this basic maintenance, i now have a ticking sound coming from the engine when i rev past 2500rpm, and gets faster the higher the rpm. took it back to the shop, they replaced the spark plugs a second time. the noise was gone for a few minutes, but came right back.

any ideas?

 

Put your hand on the fuel pressure regulator between firewall and fuel rail (canister shaped thing about 1.5" diameter), see if the noise is coming from there. If not, put a screwdriver between your ear and various parts of the engine to see if noise is from there.