My wife's 95 Envoy (Trailblazer) with the 4.2 inline, had developed a whine that can be heard above the engine noise at anything over 1800 RPM. I thought it was the alternator and changed it...wasn't it. It's pretty loud and is the dominant sound in the engine. I've used a stethoscope and the back block is quiet. The alternator makes a whine but the new one made the same sound and it wasn't as loud as what we can hear. There is some whine on the front of the block where I assume the timing belts are. The power steering pump doesn't seem to be any louder than the front of the block.

I'm afraid it's the timing belts....

Appreciate your thoughts?

Idler pulley/s A/C compressor?
Transmission??

MBHD

It was the idler pulley below the alternator...though I'd listened to that earlier but must have missed it. Bearing shot..Advance Auto had a new one in stock for 18 bucks. Wife is happy so I'm happy.

Glad to hear it was easy (and cheap).

FWIW, 4.2L cam drive is by chain.