[Tatsfield]

Based on an experience with a totally different car, so not as useful as specific experience with a Volvo, but I had a chronic screeching sound which everyone was telling was belt slippage. However it turned out to be a failing pulley and it only screeched when the air con was on or the steering was on full lock or when there was a heavy electrical load. The fault and the symptoms lay in the extra load on the belt when these systems were taking power through the belt and the extra load on tyhe pulley caused it to shriek. Replacing the pulley cured the entire problem but initially everyone was sure it was belt slippage. It was a Peugeot and it took a French mechanic in backwoods France to smile and say that it was a well known fault, well known in France anyway!