Under Dash? ticking.....

Got a 97 Silverado Z71, 5.7L. Bought this second hand and have had an annoying problem since the get go. The is a tick under that dash on the drivers side while driving. Under load, i.e. up a hill or passing, the tick gets more profound and if the engine loads up it gets heavier sounding and seems to be tied to the RPM of the engine. If you let out of the gas and coast it become barely noticable. You cannot hear it in the engine compartment or when the truck is sitting idling. It sounds electrical much akin to what you would hear when you lay a spark plug on the block to check for spark. It don't sound mechanical, but I can't rule that out cuz I just can't locate it.

Any ideas/thoughts or is this normal for this truck?

It sounds alot like the head pipe on the driver's side leaking. They will sound like a ticking sound that changes with the rpm and load on the engine but may not be audible at idle. Also, if the truck has headers, the rear area on the driver's side can partially blow out because it is usually a little harder to tighten.

I agree - you have a small leak. I replaced my muffler/converter and that solved about the same issue

Thanks guys. Was looking at a new exhaust system in a few weeks so guess I will go ahead and get the set of headers I was looking at to boot.