Noise when accelerating -any speed ('04 Tb)

Hi all, new to the board, seems to be alot of knowledgeable people around here, perhaps someone can help answer a question for me.

When accelerating, at any speed, there seems to be a 'metallic' noise, definitely related to acceleration. For example, go up to some speed, then push on accelerator a few times, as engine revs this sound appears. I may sound stupid here as it is quite hard to describe, but the best I can do is sort of metallic sounding, not grinding, not whining etc. There is no warning lights or issues with the engine at all. (I6 4.2 l).

I *think* I have heard it on other Trailblazers as they pull away from red lights, but I can't be positive. Any input would be appreciated, thanks !

I should also mention that noise is there when in park as well, so it is coming from the engine.

This might be a long shot. Check the hood prop rod to see if it is rattling against the fan shroud. Took me forever to find out thats what was making a noise on my TB. Wrapped a rubber gas line around it and noise is gone.

I had a "metallic" rattling noise with my '02 TB that would only occur when the engine was rev'd up to a certain RPM range. I would hear it most whe I was accelerating on take off.

At first I thought the guts of my catalytic converter or muffler where rattling, but with time I was able to narrow it down to the heat shield between the transmission pan and the exhaust pipe. It seems some how the head of a broken bolt came to rest between the two, and rattled when the exhaust vibrated under engine revs. That heat shield resonates like crazy with any kind of tap or movement.

Good luck.