I have experienced this first hand, it’s startling. Not only the altitude window changed by 4000’ or so the MCP hdg changed by 90 odd degrees as well. There was no consequent flight path change as we were LNAV & VNAV PTH maintaining assigned level. This happ when I was aligning the hdg bug in cruise and I def felt there was some static. And I don’t wear gloves or caps or helmets etc...