Ok so this is the first time I'm amping some mids/highs in my car using a 4 channel amplifier. I have 2 infinity reference 6x9s by an SSL F400. I bought one of those cheap amp hookup kits from walmart just to fill in the gap for wiring I didnt have. (8gauge power and rcas) I got really bad engine noise at first through the 6x9s. I troubleshoot and made a new ground for the headunit to the chastity of the car, also made a new ground for the amp to go to the same ground my battery in the trunk is grounded to. (strut ground) the engine noise was reduced but is still present. everything sounds good, but there is still some audible distortion. I have a pair of stinger bass blockers on these 6x9s supposed to block 0-300 hz @ 4 ohm, but I'm pretty sure 6x9s are 2 ohm. (it never said on the box but from what i Looked up they seem to be 2 ohm, and ohmage meter doesnt seem to want to cooperate) I have an hc1800 in the trunk strut ground with 0 gauge. up front theres an duralast platinum with big 3 upgrade, fuse block, engine ground, alt power, strut ground, all 1/0 and 0. Bass: powering an Fi Q with a mmats d300hc. door speakers are not amped therefor no alt wind is audible through them. does the RCAS used in the application make a difference? ex. using a 20$pair of stinger RCAS compared to these cheap walmart scosche stuff..I bought a new pair even though I've established that it wasnt the rcas to make the noise, isnt headunit, and isnt amp ground, but it still may be the config I have my grounds..leave to open conversation for troubleshoot. I also just figured out that the noise gets worse when I play through my auxillary cord. Well its not an auxillary its a cord adapter that uses ext in in replace of the cd changer I believe. Headunit is an older JVC KD-720. Starting to think that its the problem, but then again I'm thinking grabbing power from the back battery for the 4 channel instead of running power from the front battery is the problem? Just bought some 1/0 and going to ground the back battery to the front battery - . good idea or worthless?

Wow use paragraphs..

A little hard to understand, from what I got out of it is you have a four channel running your 6x9s and you are getting alternator whine. You also have a second battery that is grounded via strut tower. It sounds like you have a ground loop and you should try grounding your RCAs this could be another solution. Maybe a ground loop isolator, not something I would us as it is more of a bandaid than anything. Make sure all grounds are on unpainted metal up front and in back!

NOISE TROUBLESHOOTING GUIDE

NOISE TROUBLESHOOTING GUIDE

thanks dude.