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 typicall...
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A SIM card is not going to affect your audio. All it does is authenticate your device with the network. If you have data and can call, it's doing its job. I see no way possible for it to be causing this issue.

I also agree with hardware issue. If a wipe didn't fix it, it's internal and needs replaced.