Help Sudden volume problem

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My wife's Thunderbolt developed a very annoying problem in the past couple of days. Notifications/Ringtones are insanely loud and static sounding like there's an "overdrive" on for speaker sound which also distorts the sound (even at an almost muted volume). I searched through about everything I could and even found a few settings that turned out not to be the culprit (Pocket Mode, Voice Privacy). Any ideas how to set it back to a normal setting for sound?