I know a fair bit about car audio, and so does my friends. We've installed probably 10-20 big time audio upgrades, meaning new speakers all around and medium to insane subwoofers in the trunk. However, this completely blows our minds.

My friend has an BMW E90, which we ran 0 gauge through the cabin to the trunk, gave each of the 3 amplifiers (2 for subs and 1 for speakers) in the back their own separate grounds (from the seat belt). However, we experience an insane amount of alternator buzzing from the speakers. Here's what we've tried:

  • Multiple RCA cables (directly through cabin and from the doors)
  • Multiple radios
  • Clamp cables to alternator to the chassis and engine for better ground
  • A long 0 gauge wire from amplifier to battery and/or alternator (ground)
  • Another amplifier (same model)
  • Other wires to speakers
  • Speakers hooked up directly to the amplifier (to verifiy it's not a wiring problem there)

And probably some I forgot. At this point we're almost giving up on the install, as we can't find a fix. We could grab a filter or wire a resistor to something (read that a few places), but that shouldn't be necessary.

What are your thoughts on this issue? Did we miss something obvious? Can the alternator be bad, causing this to happen (I highly doubt that)?

  • Maybe a bad alternator? – Moab May 5 '18 at 23:53
  • @Moab it could be, but I highly doubt that would cause buzzing no matter what – MortenMoulder May 5 '18 at 23:54
  • Bad diodes will cause this. – Moab May 5 '18 at 23:56
  • @Moab In the actual alternator? – MortenMoulder May 6 '18 at 0:00
  • Fit a capacitor on the alternator positive terminal (3pf - not too sure of value now) this was a common solution for this issue. – Solar Mike May 6 '18 at 4:03

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