Welcome to the club! And oh man that's going to be difficult to pin down.
So you've got a manual tranny, it has a relatively new serpentine belt, timing belt, and tensioner. The noise did go away after replacing the timing belt, but only for a short time. The noise occurs when revving the engine regardless of what gear it's in.
How long ago was the first time you noticed this noise?
When I hear a squeal the serpentine belt is the first place I typically look. I try tightening up the belt to see if that effects it all. If the noise changes then it's related to the belt system, if not look elsewhere.
The serpentine belt will make terrible squeals if it's slipping on the pulleys but it's usually most apparent when the vehicle first starts up, and then quiets down after a moment. A more constant squeal could indicate one of the pulleys is failing. Perhaps the baring on a pulley has given out and is causing the wheel to grind. That happened an older car of ours and we ended up getting metal shavings in the AC system from the compressor that way.