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