I drove my '94 Toyota pickup DLX 350 miles down to Illinois over the holiday, and then a couple hundred miles into Wisonsin yesterday, when I started hearing this ticking sound coming from under the hood - directly related to the rpms. I could only hear it when I'm asking the truck to drive somewhere (if I step on the gas while in neutral, no strange noises....only when accelerating and driving). Any ideas what could be going on....I've heard rumors it could be a sticky lifter, also wondering if the exhaust manifold is leaking? It was dark and I didn't have a flashlight, so I don't know yet if there are obvious signs of anything leaking, but I'll look closely tonight.

Any ideas of what to look for and how to diagnose this?

Thanks!

Jeff