Engine growling
 

I have a 2003 3.0 liter automatic a/c mazda tribute. All of a sudden I am getting what sounds like a bearing going bad when the engine is running/idling (not sure if it does it at speed or not a little hard to tell). The sound doesn't change in intensity with a change in rpm but does seem to change slightly when the ac compressor comes on. I removed the drive belt and both the water pump and the alternator turn freely and make no noise whatsoever. I ran the heater on full and get good heat from the vents and the AC cools just fine. I don't see any type of dimming of lights nor is the car hard to crank. I appreciate any feedback. Thanks for any assistance you can provide.