Astro Van Belt Squeal

I drive for work a 2004 Chevy Astro Van It has 115,000 miles on it. A few days ago the serpintine belt began to squeal badly, so I took it to a repair shop. They replaced the belt tensioner and put on a new belt(the old one was the original)Well that lasted about 1/2 a day and the belt noise was back. I took it back to the shop and he cleaned the rust and corrosion from all the pullies and put a second new belt on it. Again after about 2 hours of driving it has started doing it again. The noise does NOT happen when the engine is at idle, only when there is a load on the engine(normal driving). The orig. belt lasted 115,00 miles with no noise what so ever. What could this be???

I would have then look at all the turning accessories, alternator, power steering pump, A/C compressor, water pump, secondary idler. One of them may to locking up causing the belt to slip over that pully.

I just also replaced the idler pully with no change to the problem. Is it possible the newly replaced belt tensioner is bad?

Anyone else have any ideas?

If none of the pulleys has a worn bearing (possibly making the noise) but the belt starts squeelling under load, I suspect there may be a pulley out-of-line.

Use a straight edge and check to see ALL the pulleys are aligned.

Are you CERTAIN the noise IS coming from the serpentine belt?

This van is rear wheel drive is it not?

Sorry I havent updated this…was out of town.
Well here is the latest update. They replaced the belt tensioner again (2nd one) No change. Replaced the alternator(Just to test). No change. Replaced the belt again. No change. Finally, the mechanic was visited by a sales rep (by chance)And he told him of this problem. He suggested he try a Goodyear “Gatorback” belt instead of the one he was using. Well that did the trick. No noise what so ever.
Hope that fixes it for good.Here is the link on them… http://www.goodyearep.com/productsdetail.aspx?id=3128

Thanks to all!

I have had the same experience. Whatever auto parts store I go to for belts, I always buy the top of the line belt – Gatorback, Top Cog, etc…