In a couple of movies characters have been blown away by speakers that have been cranked up too loud. Even to the point that they were blown through walls. Examples: Back to the Future (Marty McFly) & Teenage Mutant Ninja Turtles II (Shredder).

In both cases the characters were only stunned for a second, but otherwise completely unharmed.

No, it's not plausible. Any sound that would blow a person away would also kill them.

Also, reported again.