irritating belt squeal

[dzbowtie]

hey guys,

i know everyone knows how irritating it is when you have a slipping belt. i replaced my fan/alt belt recently so its brand new, top cog. the other is a power steering only belt run directly horizontal to the crank pulley. every now and then, one of the belts will begin to squeal like crazy, louder when gas is applied! the other night it started and i couldnt stop in traffic, so i was like "to hell with it, burn it off" lol. sometimes it only happens after the truck has run and warmed up and then i stop for gas, etc where the truck is turned off and then back on. im not sure which belt it is. the power steering belt is not a top cog vbelt, but it doesnt seem worn, and not too loose either. i have heard that power steering belts need more tension than fan belts. not sure. also, for some reason, if i turn my heater on, the sqeal will sometimes start, sometimes stopping after a few seconds, sometimes not. i dont know if there is a small change in rpm that causes a belt to slip or what. all pulleys are lined up, and the top fan belt is brand new. the power steering belt is not bottomed out on the pulleys, but i did notice i could see some of the white string near the top edge. if anyone has any ideas, they are appreciated. thanks