chirping/squealing noise

[400sbctruck]

Also, you can use the tensioner tool with the engine running.
-no squeal, but squeals when u ADD tension, usually an old dried up bearing.
-no squeal, but starts when you BARELY REMOVE tension=weak tens spring.
Squeals but goes away when ADD-weak tensioner.
Squeals but goes away when you remove tension- bearing.

Fwiw gm used k060947, k060956, k060960, and k060966 belts. Which belt u have? Last three # on belt are length in cm. last number is a decimal. If u have k060956 for example, swap to k060950(think it fits volvo if I remember right) the aftermarket stuff (usually) performs better with shorter belt due to varying tensioner pre-load. Just one of countless useless data i hope proves useful.

That adequately checks the idler-tensioner systemand allows moving on. Next stop is the alternator/ it is stressed the most in off-idle situations and such
The cam in that engine should be a roller, lobe could be swedged/brinneled, you would likely have noticed click from it ticking after full lift on the closing side. 9 out of ten times, if you check the spring it will be weak if the lobe was the problem, unless for some reason you have a flat tappet cam(lets not mention oil and additives nless this is the case). Hope i helped.