I have a pioneer 4 channel amp I connected my factory head unit in my 2013 Honda Accord. I used a PAC line out converter. Whenever I start my car I hear 4 loud bass noises.....whooomp whooomp whooomp whooomp ( I know ridiculous description but no other way to describe it. Those occur every time I start my car, then they never come back while listening to music. I can't understand what is doing it. Do you think it might be a grounding issue? Amplifier issue? LOC issue? anyone ever heard of this?
I'm no expert by any means, and in fact came to this forum seeking similar posts to my issue (not related to this). However, a quick search on Google showed a similar issue and it's a possible relation to yours (especially if your Accord has noise cancelling which I think is standard).
This post showed similar symptoms and it seems to be some sort of feedback from the mic on the speaker lines (which of course is theen carried by your LOC). Disabling Active Noise Cancellation might work.
Again I'm not an expert by any means, have only wired my cars up but it can't hurt to try!