ipod touch pops like a record?

My iPod Touch is starting to make faint popping or ticking noises when playing music in my car.

The iPod is connected via a usb cable in the armrest of my car. I hear a slight background 'pop' occasionally while listening to my music on the iPod.

I have tried cleaning the cable and cleaning the jack at the bottom of the iPod with alcohol wipes. Still pops occasionally.

I have tried doing a hard reset and resyncing my music library onto the iPod. Still pops occasionally.

I have tried moving the data around a bit by first syncing some large videos to the iPod and then syncing the music. Still pops occasionally.

I have tried connecting my iPhone 4S, which has the same music library as my iPod Touch to the same usb cable in my armrest. Music sounds PERFECT and there are no pops.

What is wrong with my iPod Touch and how do I fix it?