Alternator Noise On Car radio?

I recently installed a combo CD-Radio-Cassette deck in my wife’s car…and the unit works great! Except for the fact that it now has alternaor noise coming through the spaekers! I tried putting a bypass capacitor 0.2 mfd between B+ and ground…it didn’t help!
So what can I do to get rid of the noise?

Check how you’ve installed cables. If they’re laid right next to each other you can get noise from crossover/induction… especially if you’re using cheap cable. May also happen if you mount the cables along parts of the frame near where other equipment is grounded.

At least that’s how it was explained to me. The installation didn’t have this problem, so I reckon that guy knew something.