Need help identifing engine noise!

For starters, I have a 97 eclipse, 2.0 non-turbo, stock with the 420A engine. No mods at all.
During acceleration from about 2500 to 7500rpm, I can hear a high pitched whistling sound coming from the engine. I know it is not neither the alternator nor the PS/AC belts since I took those off and it still made the noise. I can shift into neutral and it will still do it when I rev the engine. I have also noticed it only does this during acceleration. The car does not have to be moving for it to sound. I have narrowed it down to two possibilities but I wanted to get your opinions before I started pulling it all apart. Any other questions or descriptions needed, just post and I will reply. Any help is appreciated.

check all your vacuum hoses... sounds like a vacuum leak! expecially the hose running from the valve cover to the manifold

I thought it may have been a vaccuum leak though but when I checked them, they seem to be just fine. I will check the manual though to make sure something isnt missing because that just seems to be the most likely cause. Any other thoughts out there?

my car makes the same noise i havent check yet because i like the sound of it

it sounds like its comming from the right side when im driving

i know, it sounds like a turbo charger but without the blow off valve. Reguardless I still think it would be better to locate the problem.