Oh, I overlooked the "not in motion part" ...I've never had any problems while my car is at a still-point, so I wouldn't know what to tell ya.
Have you checked the brake pads and rotors? When the brake pads are low they have a high pitched squeak or squeal, but when they are completely bad they also give off a "low, almost grumble" sound. Are they worn down to the point where metal is grinding with metal?
Again, I've only heard all of these sounds when in motion, so these are my best guesses.