This is a bug introduced between TGE 1.2 and 1.3. It is caused by something in the sound system and it only happens on some sound cards. Namely it happens on mine (turtle beach santa cruz) and no other sound cards that I've tested. There is an option for "turn off sound on alt+tab" in the audio options tab that will make it happen less. The only way to completely avoid it is to disable sound.
