Audio Systems: Crackling in speakers, crackling sound, pioneer speakers

Question
Hey, i own a 1986 bmw 735i. I bought a DUAL head unit, with pioneer speakers. When i wired them up the sounded perfect. But after i did some rewiring for my foglights they sound started to crackle. So i unistalled the foglights but the crackling is still there when i turn it up to 25. I usually would be able to turn it up to 35 with out crackling from lack of a amp. So I changed the pioneers thinking that the speakers where blown but the new speakers i bought crackled just like the pioneer. So i checked the wiring on the head unit and its perfect. But why is it making a anoying crackling sound everytime the bass hits. The bass is really low and it still crackles. Thankz
ps: could it be something wrong inside my head unit?

Answer
Depending on what the 'crackling' sound you describe actually is, it could be the headunit.  The most likely thing would be a poor ground since it did not start untill you worked on other 12v wiring.
If you cannot find the source of the problem (including trying a different headunit or at least testing it out of the vehicle), I would then suggest a total re-wire of the system. Power, grounds and speaker wiring.

Sincerely,
Jerry Mael