ok what could it be now

I went to have my car looked at today to see why it makes a loud noise when i turn it on and when the fans are on. I was told that it could have been the idler pully but it is not hooked up to the rest of the belts. So now i don't know what other options i have left. The belts are good crank pully is new. I know that the other are the orginals but i don't think that they are making the sound. Any ideas?