My car's engine won't stop ticking?

Hi, I have a 2002 Chevrolet Cavalier Z24 (2.4l Twin Cam) (LD9) and my engine is making a ticking noise coming from what seems to be the exhaust cam tower. I could be wrong, but i definately know it is coming from the top of the engine. When i'm driving around, the ticking is most noticable at a steady cruising rpm. For example, If im driving and I give it throttle, the ticking stops but once i let off alittle it ticks again and when i let go of the gas it stops, but then starts again once the engine goes back to idle (It's a standard transmission). This also happens when in neutral and gets a little louder when reving the engine in idle. I tore the engine apart and replaced the lifters because I assumed it was the lifters. While I was down there i also replaced the head gasket, waterpump, and a whole new timing set. I put it back together jsut to find out, it still has the exact same tick. The problem with this engine too, is it can be a real ***** to work on. I measured the cam lobes and like one or two of the lobes where slightly off (less then a milimeter) and I didnt have enough money to do the cams aswell considering I replaced 16 lifters, which wasn't cheap itself. The car has aprox. 204, 000 KM on it. any suggestions? Thanks!