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Q: Screeching and howling noise under the hood

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Loud squealing/screeching, howling when starting, especially first start of day, in morning. Can go away, then start screeching again with higher RPM's or acceleration.. Can go away, or continue slight screeching/whistling sound while traveling.

Did water test on serpentine belt, screeching stopped somewhat, but not completely. Installed new serpentine belt. Did not replace tensioner. Continued screeching/howling when starting. Did water test on serpentine belt, screeching subsided, howling did not. I notice what may be (with research) the AC Clutch drive plate/clutch disc? or first part I can see on compressor seems loose. there is much movement when this part is tapped with fingers. AC works fine, is rarely used here up North, maybe 3 times a year. No screeching or howling when AC is turned on or running. I can not find on Internet any noise that replicates this screeching/howling sound. I'm female, am not knowledgeable about auto mechanics. That's all i've got!

My car has 127000 miles.
My car has an automatic transmission.

A: Hi there. The serpentine belt rides on a va...

Hi there. The serpentine belt rides on a variety of pulleys, as well as the tensioner.

Each of these "rotating elements" has a grease filled bearing, typically ball bearings. Over time, the high heat of the engine causes the grease in the bearings to oxidize and dry out. In addition, the balls can wear due to the infiltration of moisture and dirt.

If the serpentine belt is new, and is riding in a plane (i.e., all pulleys and accessories are in plane and in line), it is likely that you have a failed bearing.

Note that the alternator also has a pulley, not to mention the A/C pulley and those could be the source of the noise, too. Also, it is possible that you have more than one bearing in need of replacement.

A mechanic typically detects these failures using a special stethoscope as well as tactile examination (a failed bearing will turn roughly and/or present resistance to turning). If the noisy bearing happens to seize and completely stop turning, then the new serpentine belt could snap and you would be left stranded as you cannot operate the car without the belt in place as it also drives the water pump (the water pump has a bearing, too).

Your best bet here may be to have a professional technician, like one from YourMechanic, inspect the car noise firsthand to pinpoint the problem.

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