Help with Isolating Component Causing a Crackling Noise

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Hi guys,

So, a few months back I decided that I wanted to upgrade the sound in my 2008 GMC Sierra Crew Cab with Bose. I ordered all of my equipment from Crutchfield except for a little wiring. I'll list the equipment I have below.

Head Unit: JBL Legend CP100

Front Speakers (component): Infinity Reference REF-6520cx

Rear Speakers (two-way): Infinity Reference REF-6522EX

Amplifier: Sound Ordnance M75-4

Harnesses: Axxess GMOS-LAN-02 Wiring Interface

Axxess ASWC-1 Steering Wheel Control Adapter

RCAs: Crutchfield 4-Channel RCA Patch Cables

I used Crutchfield's amplifier wiring kit, which included 8-gauge wire for power and ground with a fuse and 17-gauge wire for the remote turn-on. I did have to splice another length of power cable onto it because it wasn't long enough the way I originally had it wired. I used 16-gauge wire for the speakers. I did have to switch the brand of my wiring because I ran out of what Crutchfield sent. I wouldn't think it would matter though. My power and remote wires are running down the center of the truck to the rear seat where my amp is. The ground wire is grounded to a bolt that holds down the seat belt a few inches from the amp. The RCAs are running down the right side of the truck. The head unit is grounded through the GMOS to the chassis. We've already ruled out the GMOS harness as the issue by replacing it recently, no difference.

Okay, so now that I've overviewed the system, the issue is a horrible crackling noise coming through every speaker. With the gained turned up halfway the noise is very loud. The noise is louder in the rear speakers than the front speakers. In the last couple months I've been trying to diagnose the issue with Crutchfield.

In one test, I've disconnected the speakers from the amp and connected the speakers directly to the head unit. The crackling noise was still there, though quieter, and coming from every speaker. This would seem to point to the head unit as the issue, but when I contacted Harman's, the manufacturer, customer service, their guy told me that the reason might be that the head unit isn't powerful enough to power the speakers, causing the crackling. The tech guy at Crutchfield disagreed.

In another test, I've reconnected the speakers to the amp while disconnecting the RCAs with the gain halfway up and all filters off. So there is no input source, but the crackling is still there though it is much quieter. There also seems to be a high-pitched noise that comes from the speakers in this test. The crackling and high-pitched noise almost seem to get louder and quieter, come and go. I think my amp is well-grounded and the cable is short. This would seem to point to the amp being the issue, right?

Or is it the speakers? It does seem weird that all four brand new speakers would have issues though.

So my questions are what's going on here? and how can I definitively isolate the issue?

Harman, which makes both the head unit and speakers, has also brought me through a few of these tests, but these two I described almost seem to conflict each other, so emailing with them has been a very inefficient way to figure this out and get my warranty.

It's been extremely frustrating and having my daily driver truck's interior torn apart really *****. Any help would really be appreciated.

Hope I explained everything thoroughly, so back to the point, my questions are what's going on here? and how can I definitively isolate the issue? How can I directly test my speakers?

Thank you,


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