Ok, first off, make sure to use a battery disconnect when you're not hooked up to power and not using the unit. If not built in, they're a highly recommended add on. Until added, disconnecting the battery works too.
This is to prevent the parasitic drain from killing your batteries. Not only the radio, but the LP, CO detectors and few other devices (depending on what you've got on board) can kill them.
That being said, static (not from a radio station) usually indicates some kind of interference to the speakers. Some people have discovered weird ways their trailer speakers have been wired so it's not a far stretch to also believe yours might be lose connections, or close to electrical lines, or something of that nature. Best bet is to first pull the stereo out of the wall and to check all the connections in the back. Make sure there's no lose and no bare ones. Next, look to see if the bundle of wires is close to any plugs, etc... If so, try moving them away.
After that, if you're still having problems, let us know.
There's no use crying over spilled milk, unless it's on your keyboard.