Help Me Diagnose This High-Rev Noise

When I jump in my truck and take off in the morning in late-for-work mode (and push the tachometer needle up to around 4000 rpm), I heard a kind of chit-chit-chit sound, as if a drummer had laid down his sticks and picked up a set of brushes. The noise disappears the instant I upshift. Seems to occur to a much lesser extent later in the day when the truck and the weather are warmer, and not to occur when I race the engine while just sitting in the driveway. Would we be talking tires here? Spark plugs? At this point I don't have a clue....

 

I cringe when I see a feller hop in late for work and take off the second shes cranked over. JUST SAYIN

 

No idea from your description. The only thing I could possibly say is it probably isn't the best of ideas to start up a cold engine and then rev it up to 4000 RPM while it is still cold. It isn't doing the longevity of the engine much good.

 

Turns out one of the catalytic converters was shot (in case anyone was wondering).