Lifter Noise?

My 1994 4.3 Vortec S-10 2WD has developed what sounds like lifter noise. When first started there is no "ticking" at all, but after reaching operating temp. the engine makes what sounds like lifter noise. When revving the engine the noise increases but as it decelerates the noise disappears. The noise appears to be comming from the top, front of the motor around the a/c unit. The heads were rebuilt last year and the truck seems to run fine. Any ideas before I dig in too deep will be very helpfull.

Thanks, Bill

It could be a lifter or a valve... You can try a bottle of Lucas to see if that helps but it's only temporary...
Probably the best way is to use a steathascope and narrow it down.