95 civic radio electrical problem

I recently had the battery replaced on my 95 civic, and ever since then, I've been having intermittant electrical problems with my factory installed radio. No problem turning it on or with reception, but sometimes the buttons don't respond, and sometimes they seem to respond even when I'm not pressing them. For example, I'll frequently hear the clicking noise that means the radio is trying to eject a cassette, even when I'm not pressing that button. It's become a problem because the radio now sometimes tries to eject a cassette even when the car is off, which drains my battery. Any suggestions? All I've gotten from the shop is that I have to replace the radio. Thanks