If it was me, I too would start by wiping your phone. Since that sounds like it didnt help anything.. I would start to lean towards a hardware problem. As for the SIM card, is your audio like that only during phone calls, or even when playing music or speakerphone? Speaking from experience, a lot of reps will go directly to "Its a bad SIM card, lets change that" but in all reality it doesnt happen very often. I cant tell you how many times I've had customers come in requesting a new SIM card(as told by Tech Support), but after performing a few simple steps, the phone works great. I have even followed up with customer pertaining to this issue to make sure everything worked. Obviously SIM card failures are a case by case scenario, but typically thats just a reps first line of defense. But there are still cases where SIM cards fail, without warning or reasoning.
I have no idea if the Rezound has this options, and I dont have one here to test it.. but during a phone call, is there any options to adjust the phone speaker settings? I'm not talking about the volume.. actual settings. This may be a long shot, but maybe its something to do with the Beats Audio software?
Just tryin to help