ECU interference on door speaker

[thejimrose]

i'm no ee but did install car audio for a few years. generally you
want the shortest ground path possible. i wasn't a big fan of ground
distibution blocks, they seemed to often cause noise. might try
redoing the amp ground such that each amp or component [processors,
crossovers, etc] is independantly grounded to a well-prepped chassis
ground. make sure you clean the paint off the ground point, star
washers help the ground 'bite'. when i cared about car audio, i liked
to throughbolt as close to a framerail as possile and bolt all
rear-mounted components to the same spot. once it's all done hit it w/
a little paint to prevent rust. this 'single point' method was most
well liked among car audio geeks. each component gets it's own wire
all grounded to the same spot. keep the wires as fat and short as
possible.

another source could be the different ground points on the radio -
they usually have 3; antennae connection, chassis and electrical
[harness plug] ground. you might try isolating each to see if the
problem changes. once you find the problem you can work solutions.

i did have luck with certain cars running drain wires - from amp to
battery, and in some cases, powering + grounding the radio at the amp
distribution. you can test methods by wirignt over the carpet until
you find something that works then bury the wire once you sort it.
just be careful with  live wires in the car. fire=bad. =)