Strange scraping/grindy/whistle sound when accelerating lightly. Belts?

My 2001 2.7 4x4 5spd is making the above sound occasionally, and as the title says, mainly when I push the gas lightly. Doesn't do it when in neutral, whether driving or parked, and wont make the sound just coasting without gas. My belts need to be changed, and I read the sticky on that. At least I think they need changing, as it makes a loud squealing sound when I go over a certain RPM. I checked the tension and one of the belts does seem a bit loose. I read online that the sound along with the faint burning smell could also mean the pulley itself needs changing. I am wondering when I am doing the belts how to check if the pulley is shot? Should they spin freely with the belts off? I dont have AC if that helps, so should be just 2 belts to change if (IF) I understand correctly.Im wondering if that other sound is from a pulley thats seizing and maybe when I give it gas it puts a load on it somehow? I am a mechanic newby so feel free to laugh if that makes no sense..

 

I ended up just changing the belts out using the excellent writeup found here. Seems to have solved the problem of high RPM squealing. The other sound remains to be seen. When I drove to get the belts, that sound was gone. So hard to say if it was belt related until it pops up again I guess.

 

My first thought is the idler pulley. But could be a number of things. The best thing to do while replacing the belts, or if you decide to diagnose where it is if it pops up again, is to do the belt pull method. Where you pull one belt at a time and run the engine after each belt removed for a few seconds and see if the noise goes away with one. Hard to do especially if it's intermittent. But if it comes and remains at some point in the future, you could do that.

Could even be something internal like the water pump or other pulley inside. If that's the case, and the noise remains once all the belts are removed, that will tell you it's internal and not an external component.

But hopefully you're good with the new belts. Just throwing that all out there so you know for future reference if it comes back. Good luck.