Do you guys have your phone Bluetoothed to the radio? Every time you get a text, it does this, decreases the volume, then comes back. You don't get a text beep, just the drop in volume, and the little text icon shows up at the bottom of the screen.
Also, If you are using a headset, the VOX function will drop the volume. Could be picking up ambient noise. A cough, exhaust, wind, etc...
I hate that motorcycle they make me ride. I'm here to tell you there ain't nothing in the world I hate worse than that elephant under my ass.
Officer John Wintergreen reference his Electra Glide.
-Electra Glide in Blue, 1973-