My 2007 Trailblazer has developed a faint, high pitched whine only heard when accelerating. It is not a belt squeal, and does not happen when turning. It literally sounds like a turbo whine, but no turbo in the car. I have checked fluid levels, and they are good.
I'm concerned this is a transmission or other major issue. Can anyone give me a hint as to where to look next?

 

My 03 Trailblazer with the 4.2 did something similar. Turned out it was the fan cooling clutch. It was still under warranty and the dealer changed it for free. This solved the problem for a while as it continued to be a problem. They changed it again and later on the relay for the clutch overheated and melted ruining the fuse box and it caught on fire. Dealer said it was not under warranty and would not replace the fuse box. I called Chevrolet customer service and complained. They checked and said it was under my warranty and told the dealer to replace it.