After i start my truck if i dont let it sit and idle for a couple minutes then rev it i hear a grinding noise in the higher rpms but after its been runnin for a few minutes its fine. Anybody know whats going on?

Starter might be hanging up, and its grinding on the fly wheel.

Is it a problem i should worry about or just refrain from revving at start up

You should get it fixed if it is what i think it is. If you dont it could grind the teeth off of the fly wheel and then you would have to buy a new one of them.

Are you sure its a grinding noise? I notice a louder noise coming from the engine compartment when its drops below a certain temp (not sure what it is) but it doesnt happen all the time. When mine does it when first starting up in the morning, its the fan spinning with the engine. then after a few mins or a couple blocks it tapers off and goes back to normal..

Make sure its a grinding noise and not just the fan spinning higher than normal. I heard this once and rolled down the window and I could hear that it was the fan

Why do you rev at startup?

Oh i know i get the fan thing to in the morning too but to answer your question a1deerhunter i was messing around one day because my friend has a ford f150 with pipes and started revving so i revved back and heard it. It actually happens in drive to. If i take off to hard the sound becomes apparent.