HTC EVO 4G :: Google Navigation / Most Of Evo Reboots Itself

Wondering if anyone else has had this problem. I travel extensively on the road and always use the google nav. The problem is when a phone call comes in within 30sec. to a minute at the most the Evo reboots itself. This has happened to three different phones. I drive a vehicle equipped with bluetooth and have synced my phone to the car and the same thing happens when I get a call and answer through the car while using google nav. Was also wondering why the heck google didnt think about automatically muting the voice on the nav while in a call...it's so annoying while talking to hear the nav voice talking in your ear. The other caller can not here it but its very loud in your ear while trying to talk.