It seems with some of the newer builds during startup there is a annoying beep that happens. I at first though somthing I installed was giving an error at startup but I found that after a hard reset it happened still.
I managed to track it back to when the radio is being turned on the phone emits that beep. It is controlled by changing the following:
[HKEY_CURRENT_USER\ControlPanel\PhoneExtendFunction \CDMA\FlightModeOnOFF]
"EnableSound"=dword:00000001 (for on - the current default)
"EnableSound"=dword:00000000 (for off)
For any of you wishing to remove that jarring beep on startup (just does not mesh well with the silky smooth stability of our beloved MightyROM) just change it to 0 and enjoy.
