Is it a separate stereo from the one inside? If it is, it can be replaced by almost any car stereo on the market. If it's the surround sound stereo in your rig with separate outdoor speakers you can buy any 110v surround sound system in a big box store and replace the one in your rig.
I don't normally comment on folks "trashing" those that enjoy having music in their sites....but come on, kids playing...dogs barking....cars/trucks driving by also produce noise so noise pollution is a reality. I will always have music playing at a respectable level and shut off entirely during quiet time.
Daryll