E450 brake noise

[dsurette]

2008 Coachmen Freelander 3150SS w/2007 Ford E450 making a strange noise when braking fairly hard. With light pressure there is no problem but there is noise kind of between a groan and a hum when applying more pressure to come to a stop. The noise continues sometimes for as long as about a minute after stopping and resuming driving. Even sitting idling the noise remains and eventually goes away. I think the frequency of the noise changes with engine RPM but I'm not sure.
We're at a s&b in Oquossoc, Maine and will be here for a few days before going back to Tennessee. I will have it looked at ASAP if I can find a place that can do the work. Anybody have any ideas about what might be going on so I can know what to expect? BTW it has about 40K miles on it.
TIA

[hotbyte]

Just a wild guess, but if sound continues even after stopped it is likely related to something with the power assist side of the brakes and not the braking components at the wheels. When you hear noise sitting/idling, are you still in drive with brakes engaged? Wonder if it would continue or stop if you shift to park and release brakes.