Weird sound-RPM dependent

So for about the last week my truck has been making this whirling/howling/kind of sounds like a siren on an ambulance sound. It only happens at certain times:

1) It happens starting at 2500 rpm and is no longer noticeable (maybe just completely goes away?) at 3000.

2) It happens in all 6 gears, in neutral, and with the clutch pushed in.

3) The noise seems to only happen when the truck is warming up. Once it is at operating temp, it is no longer noticeable.

Any ideas TW?

It's a 2006 4x4 6 speed.....

 

throw out bearing

 

Ive read up on the TO bearing quite a bit and this doesnt seem to match the complaints that most people have???

 

idler pullies.

 

Possible, but I have had those going out before and its a different whine. Ill check those though.

 

Serpentine belt??

 

Mmm the belt is new in the last 10k miles....


I appreciate the thoughts, but this is a pretty specific noise and just throwing out every common whine and whirl on the tacoma is not all that helpful to me. FYI, I have thoroughly looked into this on TW before posting and found nothing, hence my asking.

I have replaced whiny idler pullys before (within the last 20k), my clutch has 110 k with no TO bearing issues (have looked into what to look for on those since it is such a common issue), and my serpentine belt is almost brand new.

I am hoping someone has had this specific problem before. IT IS ENGINE TEMP DEPENDENT. It happens in and out of gear so I am guessing bearing of some sort.

I guess to be more specific in my question, has anyone encountered this before and what did you do?