4: I’ve also experienced stuttering audio with a Bluetooth headset while moving (jogging). I am almost positive this is a hardware issue though due to poor build quality (intermittent short or open circuit). That’s not something I’ve really experienced with more reputable manufacturers (Sony, Bose for example).
Of course 2.4 GHz microwaves don’t penetrate tissue (cotton clothing is probably fine), but line of sight should not matter that much. I admit that i haven’t experimented with putting a sheet of lead between my phone and problematic headphones, but considering they work fine from the next room, I think it’s the actual mechanical jittering that’s the issue.
