ECU interference on door speaker

[Ameer Antar]

So, I finally got in there and checked out the alternator, and there it was:
the suppression capacitor was cracked. I tried wiggling the connections a bit,
and that made the noise go away... well for a couple minutes. Then the noise
started coming back intermittently while driving. So, now I'm sure that's the
problem, where can I get a replacement? Looks like a dealer-only part. Nothing
at the FLAPS or Worldpac. Can I just replace this with a good quality poly
capacitor? Thanks again for all the advice.

-Ameer