First my car is burning oil, just had the oil changed at Volvo and a month or so later I get the low oil warning, dipstick showed almost nothing, well below the hatch.
The most annoying issue I'm having is a squeal/whistle sound coming from one of the pulleys or bearings. Only does it while idling, AC on of off makes no difference but it sounds like it's coming from the AC clutch pulley? Anyone else had to replace the bearing or pulley?

 

Did you ever replaced the auxiliary belt? if so, did you replaced the whole kit (Tensioner and pully) or just the belt?
Try engine flush, maybe a few times to unclog your pistons rings, maybe it will reduce the oil burning