Garth;97191 wroteWithout hearing its difficult but would pay to check can belt tensioner those can sieze and make plenty of noise
The car's due for a timing belt change so I guess that can be investigated once the cover's pulled off, I've already got the belt (genuine Volvo) and the seals etc as it's leaking oil like crazy but haven't bought the tensioner as yet, maybe I should just buy one and anticipate changing it whilst I'm in there...
jamesinc;97193 wroteGet some soapy water and spritz the belts with it while the engine is running. If the noise disappears, you know it's belt related.
Next check the harmonic balancer. You'll need to use whiteout or something to mark the outer edge and centre of it, either side of the rubber bushing. If the marks move relative to one another, it's dead.
Next check the accessories. Disconnect them one at a time (by removing their belts) and see if the noise persists.
If you STILL can't find the source, it's probably the crank bearings.
Thanks for the detailed response, I've had the alternator reconditioned only a couple of months back hoping that replacing the bearings might get rid of the problems (it was failing anyway) but again zilch at the time. I'm going to follow your trouble-shooting regimen and see what happens, just on the spritzing I had read about this on Youtube already but have only seen it with straight H2O, I was guessing that the water made the belt grab and thereby eliminate the issue, but am wondering if the soap would lubricate the pulley and cause it to slip?