91 240 160K miles. Bought with written "bad water pump" diagnosis from Volvo dealer. Engine squeaked / screeched at idle and up. Pump pulley tight & didn't think it was bad but replaced anyway.

Thought the screech was gone but now it does it sometimes - say in 2 out of 5 starts. It usually (but not always) seems to go away on the road and after a complete warmup.

The alternator came loose recently and I thought it was that but the noise is back.

The crankshaft pulley seems OK - I read here that the vulcanizing breaks and it spins on the inner.

Sometimes it sounds like it's coming from the motor.

I should have removed all belts and ran the motor when I was replacing the water pump but was fooled by the dealer diagnosis.

Possibilities:

1. Bad belt(s): Could be but silicone spray doesn't stop the squeak.
2. Crank pulley: Maybe I just missed it in the inspection.
3. Bad alternator bearing: doesn't sound like it's coming from there.
4. Bad PS bearing.
5. Bad timing belt: It looks OK but I don't know how old it is.
6. Something bad in the drivetrain?

If it did it on every cold start and then stopped every time I'd suspect a bearing or other problem with the cam. I've not had this kind of problem with any of my 240s.

Other possibilities?
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240s: 2 drivers and some parts cars

Check the trueness of the belts as they run from the Water Pump pulley to the Alternator. The alternator can tweak a bit so the Alignment is not true. That will cause this squeal until the belts heat up and soften.

This is generally caused by the bushings Alternator bracket wearing out.
You can loosen the Pivot bolt on the Alternator, Push the alternator back toward the engine to Align then Tighten the Pivot bolt as you hold it.
It take three hands to do easily but you can manipulate it by yourself.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

Old hard belts will squeak, mark both parts of the harmonic balance and see if the lines separate. Although not part of the squeaking if you don't know how old the timing belt is replace it, any leaking front engine seals, the TB tensioner, and all the drive belts. When the belts are off check the accessories for free spinning bearings. Dan

Belts are new and seem supple. Timing belt I don't know - I have a new spare so maybe I'll do that anyway. But I don't find anyting here about a timing belt squealing.

I did check for free spin when belts were off but that's just alt & water pump.

Good idea on marking the balancer.

'll read up on the TB tensioner. I didn't think of that - never fooled with one.

No leaking front seals; I did replace water pump.

Thanks for the comments
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240s: 2 drivers and some parts cars

Timing belt or the tensioner won't be part of the squeaking problem but for dependability concerns it is a good idea to replace it before it fails and leaves you stranded.
If the belts are new and properly adjusted the problem will most likely be the harmonic balancer.
Dan