Is the LOC adjustable, if so try turning its gains down and adjusting the gains on the amp. There is no need to max them out, the deck supplies a healthy amount of voltage. When I was using a Pac Loc when I still used my factory deck, i had it set around 1/4 of the way up, roughly 3ish volts of output.

 

So I checked this morning and I am using the PAC SNI-15 which does not appear to have any type of gain control. Yesterday I also disconnected the power and ground from the amp and tried it again and I still get the alternator whine, so I would think that would rule out my amp as the problem. I also tried disconnecting the RCAs from my LOC this morning and still got the whine so I think that rules out the RCAs being too close to power wires. I guess this only leaves the LOC and the splices in the wiring as the possible culprits, unless I'm overlooking something here.

 

With the power off, disconnect the rca's from the amp, power up the system, if you still have noise, its either your rca's (possibly pinchedor just cheap, non shielded twisted pair construction) or try adjusting the gains down on the amp, if this dosn't help then check your speaker wiring to ensure their not pinched and then, worst to worst pull each speaker and ensure where the wires connect, their not making contact with the door.

 

What type of head unit do you have? I had a problem like this and found out Pioneer head units are notorious for the whining sound when having RCAs plugged into it. You have to ground the RCA ground to the head unit. Sounds crazy but fixed the problem. We looped a wire around the outside of the RCA cable and grounded it to the head unit chassis.

 

I'm using the stock radio. I had an extra set of RCAs at the house that have never been used before, so I swapped them out this weekend and ran them a different route than the previous set just in case the first set was picking up interference somewhere, getting pinched, etc and still have the same issue. Even when I unplug the RCAs from the LOC I still get the whine, which was not present until I installed the LOC. So I think at this point I'm going to have to un-solder my LOC connections and swap out the LOC for one of the adjustable ones. I just can't figure out what is causing this, but it seems like it is narrowed down to either the splices picking up interference or a bad LOC. If that doesn't fix it then I am completely lost.

 

Do you get the noise when you unplug the rcas from the amp. If so the issue is not the loc but further down the signal chain. If this is so, start disconecting one speaker at a time an see if the issue goes away. It may not be the loc but the amp or a speaker. Does it only happen when the vehicle is running?

 

Ground the amp directly to the battery's negative post. You'll need extra power cable or use a set of jumper cables to make the connection. If the noise goes away you have a ground loop and need to find a better place to ground your amp. That or try a ground loop isolator.

If you still have the noise re-ground your amp and disconnect the RCA cables from the HU and plug shorting plugs into your amp's RCA inputs. Shorting plugs have the barrel and center pin shorted together. Installing them in the amp's inputs gives the amp the equivalent of a zero volt input. Turn the amp on by turning on the HU or by placing 12V on the remote turn on lead to power up the amp. If there is no noise after starting the engine you'll know that the noise is entering your system upstream from the amplifier and it is not the problem.

Do your RCA cables use twisted pair constructions? They should. Twisted pair construction helps to prevent noise from entering the signal. Shielding alone won't get the job done.

 

Okay so I tried adding a Ground Loop Isolator but it did not seem to help. I double checked and my new RCAs are twisted pair, not sure about the old RCAs I was using previously. I guess my next step will be to try grounding the amp directly to the battery so I will give that a go this weekend.

 

Bringing the ground back to the battery will isolate a ground issue on the power side. An rca isolator eliminates it on the signal side... Also make sure you have quality wiring with good insulators...

 

Okay so I finally got around to re-grounding the amp, it is now grounded to the negative terminal on the battery. Unfortunately even with the amp grounded to the battery and with the addition of a ground loop isolator on my RCAs I'm still getting the alternator whine.

Taking into consideration that there was absolutely no alternator whine prior to me splicing into the factory wiring to add my line output converter, I decided to un-solder my splices and then I reconnect all of my splices and make sure that they were all taped up and ensured there were no wires left exposed. I also made sure when I put everything back into the dash that there were no wires being pinched. Still getting the alternator whine.

The only thing I can think of is that either I have something wrong (pinched, cut in the insulation, etc) with one of my factory wires and I'm just not seeing it, or my line output converter is the problem. Anybody have any other ideas? Also does anybody known why the whine is only present when i use OnStar or Bluetooth? When using the aux input if I plug my iPod into the cigarette power adapter you can hear the whine faintly in between songs, but its nowhere near as bad as it is using OnStar and Bluetooth.

 

Why did you ground it all the way back to battery again? I've always been told that the shorter the ground the better. IMHO I would have went to a seat mount or seat-belt mount...

 

I have my amp under my seat as well and I also use a line out converter, I did not have to ground my line out converter but I have my amp grounded to the seat belt mounting bolt

 

Originally I had it grounded to the seat mount under the driver side rear seat, and it was suggested I try grounding to the amp back to the battery. I'm hoping that replacing the LOC will fix the issue because at this point i'm out of ideas.

 

Just as an update, I finally figured out what the problem was and now I am able to use my bluetooth and on-star with no alternator whine. After trying all the suggestions I got on here (And I do appreciate all of your input) it seemed as though the only thing left was the LOC. I finally got around to buying a new LOC (Scosche SLC4) and replaced the old LOC (PAC SNI15) today on my lunch break. Turned on my truck hit the bluetooth button half way expecting to hear the dreaded whine, and to my amazement there was no whine. The music from my amp sounds just as good as it did before, only difference is there is no whine. Thanks again everyone for your help!