This started happening a few months ago, seems to only do it when the engine is cold and less than 1500 revs. I actually thought it was the alternator when it first started happening but I'd only heard it while sat in the drviers seat. Yesterday for the first time since it started happening I had the engine running with my head under the bonnet and realised actually the loud (very loud) high pitched whining/squealing is coming from the wrong side of the engine for it to be the alternator:
I can't seem to find an exploded view of this side of the engine with all the components labelled, so correct if I'm wrong please but is that the belt that drives the oil pump and the timing chain? If so, my guess would be the oil pump's making the noise and probably has a bearing on the way out? It doesn't really sound like the belt is slipping (and considering my current misfire issues I'd be highly surprised if it was something as simple as the belt slipping or the tensioner causing the noise).