I have been battling with this high pitched squealing noise coming from somewhere within the engine bay of my 2012 JCW R56 Hatch for the past few weeks. It is very hard to pinpoint where the sound is coming from due to the sound only occurring while driving going between 4,000 RPM to redline, and will get a higher and higher pitch until reaching redline. Also, if I slowly creep up to 4,000rpm+ there's little to no squeal. No squealing while idling or even giving it gas at a stop. I would think if it was the water pump or tension pulleys it would do it more constantly or at lower RPM. The S-belt was replaced only 10,000 miles ago so I think it's very unlikely it is that. Could it be a diverter valve or some type of boost leak to not give a check engine light or any decrease in power? It seems to me whenever there is boost built it up it makes the sound. If anyone has ideas or opinions I would appreciate the help! Thanks!

 

any update?

 

Doesn't mean that the serpentine belt is not slipping, especially at those rpm. I have change the belt on my daughters 3 times now in 5000 miles to see why it slipping. Have change all components that have to do with the bel, except for the crank pulley and ac clutch. Gonna change the crank pulley and 3rd belt and hope this work. If it the ac clutch the car is going up for sale.