Classic symptoms of an imperfect seal. Speaking only for myself, the seal has to be far more than just enough for the bud not to fall out -- it has to be good enough so that a hand clap is inaudible. Sounds like you're using the wrong tips, or not seating them deep enough, or not putting them in your ear correctly. With music playing through the buds, push and rotate them, try to find a deeper spot in the canal where bass content suddenly shows up. That's where the tips need to be located. A too-small tip will never seal no matter how deep; a too-large tip will seal but will dislodge with a quick turn of your head or a change of facial expression (like a smile). I spent a LONG time choosing which tips would a) seal and b) stay sealed.
Though the buzz could be driver overloading due to compensating for a bad seal with more volume and/or more bass, it could also be a gain stage problem up the chain. I've seen the latter problem where the summed feed to the belt pack is too hot, so the belt pack overloads and starts distorting, especially down in the bass region. We generally run the packs wide open and cut back on the gain up at the transmitter or the signal feeding the transmitter.