I have a 2003 Subaru Forester with 240K miles on it. When I start the engine in the morning, there’s a squealing noise under the hood that lasts for a few seconds. (Usually goes away as soon as I pop the hood and look at the engine.) I think it’s one of three things: AC compressor, alternator, or power steering pump, but I haven’t been able to isolate the noise to one of the three. I don’t want to wind up replacing all three. Any suggestions?
Replace the serpentine belt and when you have thew old one off, rotate each pulley by hand.
The crankshaft will not move, but if any others are hard to turn or rough sounding…there is your problem. But it could just be the belt alone that is the problem.
Just to throw something else out there, it’s also possible this noise could be related to a timing belt tensioner or water pump.
You might consider removing the serpentine belt and noting if the noise is still present.
If it is present with the accessory belt off then you really need to start worrying about an issue in the timing belt case and the ensuing damage if something comes apart in there.
Good catch @ok4450.
It does sound like the cause is likely something to do with the accessories. Another idea not involving removing anything is to use a mechanics stethoscope to isolate where the noise is originating. I use a length of old garden hose for that purpose. Tom and Ray have suggested using vacuum hose.