What can make a metal to metal screeching or grinding or rubbing sound. It sounds like turbo housing/wheel contact, that type of sound. I checked the shaft and it is fine, but the sound I heard resembles that. It isn't constant or consistent. Going down the highway today I heard it when I let off the throttle, lasted maybe 2 seconds then went away. Only did it maybe 2 times on my 1 hr trip. I have heard it before, like last summer. It sounds like it is coming from the motor somewhere. Just looking for ideas that you guys may have run into similar sounds/problems before.