Squeaking from belt or pulley

First of all, do not use any type of belt dressing in a can. That will make it much worse and that stuff will collect dust and road dirt, then the squeaking will be worse. The only fix for that is to remove the belt, scrub all the pulleys with soap and water, then install a new belt.

I never heard of using baby powder before. How many babies does it take to get a quart of powder?

The next time you catch this noise occurring, leave the engine running, then dribble a little water on the smooth backside of the belt. If the noise changes, it is indeed an alignment issue. If the noise does not change, a better suspect is a bearing in one of the pulleys. Spinning them by hand will not show that up because there is no sideways pressure on them.

When misalignment is the cause, a pulley is tipped or turned a little. That makes the belt walk across the pulley as it goes around it, and that is what sets up the squeal. As little as 1/16" is more than enough to be heard. It is caused either by the pulley where the squeaking occurs, or the pulley right before it. The culprit will almost always be one of the smooth pulleys. They usually come painted black, then the paint wears off where the belt runs around them. Inspect them to see if the belt is running on the paint on one edge, or if the shiny area is wider than the belt. If the belt is riding on about a 1/16" area of paint, and that small strip of paint is not worn off, the culprit is likely to be the previous pulley. If the entire area the belt is riding on is shiny, and that area is wider than the belt, it is more likely that is the pulley with the problem because rather than just running off-center, it is sliding across that one, and that is what wears the paint off very quickly.

Another way to search for this is easier to do than to describe, so I drew a sad drawing that might help. When you look perfectly straight down from over the belt, you should only see it on the highest pulleys. In my drawing, the belt can be seen peeking out to the front just a little. That is the part shown in red. This could be the water pump, or more commonly, an idler pulley. It is sticking out because it is off-center on that pulley. Tension-er pulleys swivel on a mounting bracket, and that is a good place for wear to occur that lets the arm tip. Solidly-mounted idler pulleys can develop slop in the bearing that lets the pulley tip.

Also, check the belt tension. I highly recommend doing this with the engine not running! Tug on the belt to make the tension-er pulley move to the end of its travel, then release the belt slowly. The tension-er should immediately take up the slack and pull the belt tight. It is not uncommon to find a tension-er that is rusted tight and will not move at all. It will not keep the belt tight as it wears and becomes loose. If it is reluctant to move all the way back on its own when you release the belt, it is becoming tight and will occasionally bounce to release tension, then fail to fully tighten right away. Sometimes just exercising it by tugging repeatedly on the belt a dozen times will free them up for a few days. That can be long enough to identify it as the cause of the noise.

The grooves in the pulley should be deeper than those on the belt. The sides of the ribs are supposed to wedge into the sides of the grooves on the pulley to help the belt grab it better. If the belt's ribs were able to bottom out on the pulley's grooves, it would slip over the pulley without grabbing it.

If there are chunks breaking out of the belt, check for cracks across it. Serpentine belts are considered to be okay if there is less than one crack per inch.

That verifies the belt is sliding across a pulley. While this is more common on four-cylinder engines, look for a component that is mounted on rubber bushings to reduce vibrations. If you see anything like that, try prying back and forth on it to see if it affects the squeal.

Typical "component" would be the generator. They are often mounted on rubber bushings on four-cylinder engines. Chrysler had a service bulletin for a belt squeal in the early '90s. The test was to pry it one way, then the other, with the engine running, to identify which way it was turned a little. The fix was to add a washer to the mounting bolt to reposition the alternator. The fix only took a couple of minutes and was real effective. I did that on two cars.

V-8 engines don't usually have this problem, but it's something to not overlook.

Since the tensioner is new, that is a good suspect. They usually have a tab that sits in a hole to keep it in proper position. Corrosion can develop in that hole, especially when the hole is in a plate of aluminum. Check for any debris that got overlooked and caught between the mounting surface and the tensioner's mounting plate.