My 2004 Prius makes a loud, consistent SQUEALING NOISE from the engine compartment, only when I increase the ICE RPMs a little by stepping on and holding down the gas pedal. Car is in Park and not moving (it also happens when car is driving, and ICE revs above idle). It sounds like either something rubbing, a bad bearing, or a vacuum leak. I looked everywhere. I removed the serpentine belt and the noise still happened when the ICE is sped up, so it's not an idler bearing, the waterpump, the belt, or anything driven by the belt. I changed the engine oil. The transaxle oil looks dark red but clear. Someone said it may be the MG1 or MG2 bearings. Others say vacuum leak. It is really loud and sounds like it's from everywhere -- engine and transaxle and electric motor and inverter. It does not happen when the ICE is off, or idling. Any suggestions would be great.