I bought one of those Amazon bundle packs for 10 dollars with the stereo, fm transmitter, and a cleaning cloth, but it hums when the music is playing and when the music is not playing. Why?

Here is how it looks:(but it doesnt say Prolynkz at the top, it just says "wireless fm transmitter"

http://cdn.overstock.com/images/products/3/P113451...

I'm trying to use this in the car or with my radio inside my house or wherever. Is there something more suitable for this?