Whistling / Whirring noise, varies with RPM
 

I've got an interesting noise coming from the engine bay, the best way I can describe it would be: sounds like a field full of crickets in the engine bay, and it varies with engine rpm. There's a higher pitched 'whistle' too, but I don't think that's anything (correct me if I'm wrong). It's the 'field of crickets' I'm after.
I can't pin down where its coming from, but it sounds like the front/top of the motor itself. Maybe more prominent on the turbo side? It almost sounds like a belt to me, but I just don't know. I'm looking for second opinions before I go taking things apart, on the off chance anyone has experienced this.

I've been hearing it for a while now, but it seems to have gotten slightly louder? Maybe I just care more because I've dealt with some of the more pressing issues. I notice it most driving past buildings or guardrails where the sound comes back at me from one side or the other. I really wouldn't notice it if it wasn't so damn loud..

The car is very modified:
- emissions equip. removed
- ac + heater removed
- aftermarket IC, rad, intake, tubing
- 850 primaries, 1300 sec, twin power, power FC
- downpipe w/ no cat, 3" resonated pipe back to muffler
- simplified sequential w/ stock twins
- probably something else important I'm forgetting

My guess is that the alternator bearings may be bad. Remove the belt and start the car. See if the noise goes away.

Exact same thing I would suggest trying. This will immediately tell you within minutes if the noise is related to anything powered by the belt. super fast / easy check.

A chirping sound? If not a belt, might be the clutch release cylinder going bad or already so. Keep an eye on the brake fluid level, see if it is not gradually being lost.

My guess , aftermarket flywheel

Oh that would drive me nuts. Get one of the stethoscopes with a metal stick end on it from harbor freight and start touching it to everything with a moving part on the engine. Helps to troubleshoot bearing issues for me.