Wondering if anyone knows what might be causing a loud high pitch whistle from the back of the engine bay at idle? I’ve read that water pumps going out on some Minis has caused this sort of noise and that could be my issue. That said, when the whistling is occurring, if I pull the oil dipstick out a bit, the whistling stops. I put it back in and the whistling starts again. It seems that relieving the pressure by pulling the dipstick stops the issue which wouldn’t seem to be a water pump to me. Suggestions?

 

any loss of power or anything? My first thought is vacuum leak, especially with dipstick removal stopping the whistle.