I am surprised no one has yet given you the search or die comments. ;O) In Baffels sticky at
http://forum.ppcgeeks.com/showthread.php?t=42730 he says that doing a hard reset on the phone may remove this problem.
I have tried it on my Sprint version to no avail. I use this mostly with Bluetooth or in the car with the radio where their is no problem so I doubt it is the software. I have contemplated taking mine back but it works so much better than my Mogul in many other ways I am thinking I might live with it.
Zarlof.