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Q: Squeal when engine starts or revs.

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So when we start the engine, there's a squeal, but it goes away when the engine idles. The squeal comes back when you rev it, but if you hold the revs steady, the squeal gets quieter. We've replaced the serpentine belt, tensioner pulley, and idler pulley and have replaced all fluids. Out of ideas on what else the problem could be. The truck drives fine; there's no odd vibrations or other sounds coming from the engine compartment, and no strange smells. So if you guys have any suggestions of what it could be, that would be greatly appreciated. If not, we'll just throw in a new one. Thanks!

My car has 250000 miles.
My car has a manual transmission.

With having already replaced the belt and the idler and tensioner, I would look at the components next. Something like the bearing or bushing going out in one of the other driven components. The alternator, the power steering pump, or the air conditioning compressor could have a bearing/bushing that is beginning to fail, and can cause a squealing sound like you have described. Also, if one of the pulleys has a "glazed" surface, it too can cause a squealing sound. When confronted with this type of issue, I would normally have a partner start the vehicle and try to replicate the issue while I would use a stethoscope to identify exactly where the squealing is coming from. If I didn’t have a stethoscope available, I would use a length of brake line, a piece of hose, or something similar, to isolate the sound to my ear. Obviously, you need to be very careful not to come into contact with any of the moving parts, but about anything hollow, and of adequate length, will suffice. If this is something you feel you could use a hand in identifying, or repairing, contact a certified mechanic, like those available at YourMechanic.com.

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