My 2004 Pontiac grand prix has a steady clanking noise from the engine and gets worse with acceleration. Any ideas what it might be?

Loud? Thrown piston rod, broken valve stem or such,.....not so loud? Valve tappets, something on serpentine belt pulley, there is a LOT of guesswork here

Did it come on suddenly (cracked flywheel), or is it getting worse over time ? (rod bearing).

Happen suddenly. I was going 75 thru I95 from jackson mi to BC mi and back and it just happen

Well both my bosses just saw my car and claimed its a piston rod and motor. Idk

Piston rod bearing is a reasonable guess. There is virtually no test to confirm this without tearing down the engine. If the engine is running okay other than the noise, its worth fixing.

While I generally agree with Norm's advice I'd disagree on this one. It's 10 years old and not worth much. There's a ton of hours involved in a job like that plus the parts. I'd start looking for another car.

Thanks Munron, yes it is a lot of work. The 3.1 engine was very popular and is available all over the place. You can get a running engine for as little as $300. But the total labor to replace a rod bearing might not be worth it. Before trashing the car, I would pull both valve covers and make sure it isn't something easily fixable,such as no oil pressure, a stuck valve, bent pushrod or collapsed lifter. Just because 3 people say it "sounds like a bad rod" doesn't mean that's the problem. Dig a little. Good luck!