This fits in with my experience. It seem's that this problem is exacerbated by high temperatures. My s6 is fine here in Ohio, but on a recent trip to Utah and Arizona I would get the buzzing when the temps reached up near, and past 100.
Count me as another who sees outside heat as a trigger for this problem. At home in Ohio this has never happened. But while on vacation a few weeks ago in Utah and Arizona, it happened several times. Every time the temperature was in the upper 90s to almost 110.