Probably a ground issue somewhere. I was trying to stay stock, but ended up putting in a new to me head unit (couldn't take no tunes anymore). But to keep the stock look when I go to shows, I went with this (you can hardly tell it's not real).
Blaupunkt now makes a retro stereo that looks virtually stock in '80s European cars but it's nearly $500, and offers the same features as a $150 Kenwood Excelon, which absolutely has higher-grade internals. It's highway robbery, but it does look good.