Belt noises on Mazda 3
 

For my son's 2007 Mazda 3s, we were getting a lot of belt squeals. We replaced the tensioner pulley and both belts (with the good belts that are not supposed to squeal) Still if he accelerates hard and also around 60 mph we hear an occasional squeal. Any advice?

Are the pulleys glazed?

I'm not sure what that means. Can you please elaborate?

When the belts slip on the pulleys, the heat and friction will leave behind a shiny deposit that will make it difficult for the belt, old or new to get any grip on it. Prolonged slippage will exacerbate this. Just a thought.

The pulley closest to the tensioner pulley is shiny. What can I use to remove the deposits (that won't harm the belt)?

Try a little Emory cloth. Rough it up a touch.

Thanks for that tip. Will give it a try tomorrow. I saw someplace else that showed putting a little automotive polishing/rubbing compound on both sides of the belt. Any pros/cons of this method?

The object is to break the gloss and/or clean the glaze off the metal, so they could work as well.

Also check idler pulley (most likely; they often fail with the tensioner) and the alternator, air compressor and power steering pullies spin smoothly and freely (remove the belts to check).