squealing noise coming from under hood...?

It might just be the belt. To test this, spray a little WD-40 on the belt while the engine is running. If the squeak goes away, replace the belt.

Danielle, Please disregard what Ben said. Never spray an oil based lubricant on a product (belt) made of rubber. It will absolutely shorten the life and eventually rot the rubber.

You may want to buy a can of pure silicone spray at any auto-parts store. Lift the hood and liberally spray the underside of the flat serpentine belt with the motor running. Serpentine belts can be tricky as some last 60,000 miles and others start to show splits on the driven (underside) much sooner. In that case it needs to be replaced ASAP.

I hope the "boyz" at the dealership removed the belt and spun all the pulleys by hand to see if there was a bearing issue in the alternator, power-steering pump, water-pump, idler pulley and *serpentine belt tensioner pulley - which has no real bearing as such in it. The actual tensioner may be OK but the crappy sleeve bushing inside may have crapped out.

Wish someone who really cared could take some time to fully inspect your problem. It sure "ain't" hard to find but the "jack-asses" need to be interested enough to really look. You may want to leave the car at the dealership overnight and have then start it up in the AM in order to reproduce the time of day when the noise occurs.

WD40 is not the answer. The answer is to tighten the belt. The alternator is affixed to a bracket that has a "oval" hole(its the words that come to me to describe a hole that is used for moving the alternator inward or outward or adjusting) You need to loosen the bolt that shows on the one side of the hole and then you can move the alternator outward with a pry-bar or large screwdriver so that it is pulling harder against the belt. Possibly the same story for the power steering pump. And possibly the same story for the A.C. unit.. I say "possibly" because if all 3 things were using 1 belt to drive them; then you only need one adjuster. Belts can be compared to new shoes. They fit tight when new, but after you have walked in them a couple of years they fit like slip-ons, or just downright sloppy as the material has stretched. Really, a minor adjustment. But then again, some people will drive them for years squealing away. At this point the belt is glazed over with the years of slipping and it is better just to replace the belt with a new one. That is all I can tell you is wrong with that part. Even car sales people have their own mechanics so he would know that is all that is. His low price is for another reason. Closely inspect the bodywork. If you do not feel adept at analyzing the mechanics of it, try to bring an all-around mechanic you trust with you to give you his impression (he can't make a guarantee) it is only what he sees and hears outright to advise you. May cost you a few bucks for his time. Go from there.

Squealing noises are often caused by worn belts. Try to figure out what causes the squealing noise to start. Sometimes when you just crank your engine worn belts squeals for a while then stops. Other times when you turn on your a/c worn belts squeal once again. A squealing noise can also be caused by a worn bearing on your alternator or a tension pulley. Check the amount of miles on your vehicle and if possible have the belts replaced. Good luck!

It is a slipping belt. The belt could have stretched a bit or it might have become glazed (slippery) and now need to be replaced or it could be pulley tensioner spring. Try turning the steering wheel to the lock either way and see if that causes it to happen. Your dealer may have given it the "sunshine test". Leave it outside for a day and say they couldn't find anything. I think if they looked they would have found the problem.

At what point does the noise start? Is it cold or after you have run the car for a while? You might try taking to a different dealer if there is one close enough for you to go to. Unless the car is making the noise at the right time it will be hard to get them to listen to you as like most mechanics they think they know everything.

If it is not the spring then the serpentine belt might be worn. Check for cracks and glazing. If one of these are present, then the belt is gone.

Depends on weather conditions is the reason the belt will not squeal.

It could be your fan belt or a water pump. But I think your car is to new to be the water pump.

It might be something wrong with your struts or you might have a broken front axel grinding on something.

Is your fanbelt slipping?