I just wiped out my second Garmin 305 Forerunner. The sound is gone. I've concluded that for some folks sweat wicks up the speaker holes, and the moisture and salts from the body corrode the speaker. The sound fades and basically goes mute shortly thereafter.
Has anyone else had that problem and what have you figured out a solution? Other than switching to a new device?
This is a very common issue with the 305. And by no means is it limited to the 305; other Garmin watches and other brands also encounter the problem. It's just the nature of subjecting a watch to the elements of a running environment. If your 305 is still under warranty, I suggest taking advantage of it by trying to get a replacement.