strange buzz/rattle @ 3K

I got a 03 Trailblazer. Every once in a while, I hear what sounds like a cross between a buzzing sound and a rattling sound around 3000 RPMs (no it's not pinging either). It seems to only happen if the engine is half way warmed up or cooled down slightly depending how you look at things. If fully warmed up I never hear the noise. Likewise if it's cold I don't hear it either. It seems to only happen like if the thing is fully warmed up, then I stop at the store or something, get back in and take off. Around 3K I hear the noise until the thing hot hot again. Any ideas?
Thanks

And this is driving, idling, accelerating, key info missing here, from front, back under the hood?

[QUOTE=jkomatsu]I got a 03 Trailblazer. Every once in a while, I hear what sounds like a cross between a buzzing sound and a rattling sound around 3000 RPMs (no it's not pinging either).

Try this, open the put a hood a piece of fuel hose over the hood prop rod. Place the hose at the point where the rod comes close to the fan shroud. This worked on my 04 LT.

Rob

And this is driving, idling, accelerating, key info missing here, from front, back under the hood?


The noise happens when driving. Not sure if it would happen if I simply reved the engine when sitting still.
Sounds like it's coming from under the SUV; maybe halfway back.

[QUOTE=jkomatsu]I got a 03 Trailblazer. Every once in a while, I hear what sounds like a cross between a buzzing sound and a rattling sound around 3000 RPMs (no it's not pinging either).

Try this, open the put a hood a piece of fuel hose over the hood prop rod. Place the hose at the point where the rod comes close to the fan shroud. This worked on my 04 LT.

Rob


I'll try that. Thanks

I'll try that. Thanks
Also check the seseral exhaust shields for looseness or contact with a pipe.

I had a similar noise coming from the front end of my 04 TB. It was really noticiable driving down a rough road with the windows down. When I got home and checked the front suspension and noticed that when I tapped on the inside plate that covers the dic brake rotors, it rattled. The bolts were tight so I "slightly deformed" the plate. Noise gone!!