Weird Problems with Front Panel Audio Connector

A couple of weeks ago I began having a really strange problem with the volume of music on my PC. While listening to CDs or MP3s, on several different players, the music will go through very noticeable swings in the volume level during songs. It's very, very weird. I have no idea why it's happening. It happens no matter which player I'm using or which MP3 or CD I'm listening to. The volume will all of a sudden get really loud, and then get really quiet, and then really loud at seemingly random times. It's driving me crazy.

I only began having this problem after I connected the front panel audio from my case to my motherboard. I wanted to start using the front panel headphone jack. This is when I began having problems.

Today, as an experiment, I unplugged the front panel audio connector from my motherboard to see if the problems still occured. To my surprise, I was no longer able to get my computer to make any sound whatsoever. No sound would come out of anything that I plugged into my soundcard. I then reconnected the front audio connector to my motherboard. The sound mysteriously began working again. MY SOUNDCARD ONLY WORKS NOW WHEN THE FRONT PANEL AUDIO CONNECTOR IS PLUGGED INTO THE MOTHERBOARD. How is this possible? Why is this happening?