I'll start by saying that I used to think I knew a small amount about mobile audio but like everything else the more I learn the less I actually know. I searched both this forum and the headunit forums and have done a fair amount of testing but am still having some issues. Here is a run down and hopefully someone can help me get rid of the engine noise.

The truck is a 08 with basic cd/mp3 radio in an fx2 screw.
I have a 6.5 component set in front and replacement coaxials in the back. The amp is an alpine pdx 5 channel. I also installed an pioneer ibflat 10.
The headunit is factory with a pac 4 channel loc. The wires are 4 gauge power/ground memphis kit with twisted rca cables. The power is run done the drivers side and ground in passenger side. The amp in under the passenger rear seat.

Testing:
I first plugged my mp3 directly to the amp and most of the noise if not all of it went away.
Since that cleared most of it up I pulled the head unit and checked the pac and regrounded the unit. I tested the ground at .8 ohms. (My test wire had .4 in it the numbers are minus that) I went ahead and added another ground that I bridged off the 12v plug in (lighter) since I dont use it and it tested at .6 so I tied it to the pac. No change.
I tried adjusting the pac down as it was set at max and increased the gain at the amp and that cut down on the noise.

I did notice that the noise changes with things in the truck. If you open the door it hums, turn on the dome it changes pitch and if you roll down the window it changes. These things would lead me to beleive it's a ground issue but testing seems to say it is ok. Do I need to check the amps ground even though the mp3 plays clean through it?

A side question on adjustments is it better to have the pac one way of the other on it's adjustment? Seems like when it's lower and the amp gain is higher the noise is reduced.

Is there a right way to hook up the sub channel when I only have 2 pair of rca through the convertor?
I'm using a splitter atm off the rear channel and it works ok I guess. The noise was there before the splitter was installed.

 

Are your RCA cables run anywhere near your power cable? Thats usually how people get engine noise through amplifiers.

 

I have the power going through the drivers side and the rcas come down the passengers side. They only get close at the amp.

Looking into grounding the stock radio case.

 

Did you ever get this fixed Dag? I'm looking into getting the PDX-5 myself, because I just want enough power to fill the cab, not wake the neighbors. I'd say it's because I'm too old for that sort of thing, but even at 20 I wasn't that brand of asshat that needed to share my music with the rest of traffic half a mile away.

It sounds to me like the problem is your source, not your wiring or your amp. My first bet would be the PAC LOC is faulty, but it could also be something wrong inside your head unit. If this were a computer, I'd remove everything, then put components back one by one until I found the weak link in the chain.

 

The PDX amps are notorious for having floor noise, but it will just be a constant hiissssss when the volume is down all the way or between songs, it should not change pitch with the engine RPMs. If you have alternator whine it is not the amplifier. You likely have a ground loop.

 

Well crud Sal, I was really looking forward to installing one of these. Wonder if the new V60 that is coming out in April is going to have this same issue? Guess I'll have to deal with stock a little while longer.

 

It shouldn't be overbearing, just a very slight hiss when the system isn't playing music. It won't bug most people but for those that are picky about their sound it will be. I do not know if the newer versions have this problem or not.

If you are set on a 5 channel you may want to look at the JL 900/5 or the Zed Leviathan (technically a 6 channel, but you can bridge channels 5&6 for 600w on a sub). The new Massive audio NX5 is also a beastly 5 channel worth looking into. (if you want the NX5 let me know, I can hook you up with a sweet deal on one).

 

I never got it to go away. Now my other issue is if I crank it up for very long the stock headunit shuts down.

The pac isn't helping things and I regrounded it and also grounded the case of the stock unit to try and eliminate any ground loops. I also grounded the outside of the rca cable end but the noise was still there.
Overall though i'm happy with the pdx and know the stereo will only be as good as the weakest link. The headunit at this point is the weakest link and it shows. I'm considering a pioneer 4300? with the bigger screen.
Don't think the amp will only help fill the cab! Mine is 4x94watts rms and 1x402rms. It pushed the components to the max and is over the max for the coaxils and the sub. My gain is less then half on the speakers and like 3/4 on the sub. Bottom line is the truck is plenty loud for those inside as long as you're not trying to rattle your teeth out with bass. The mids and highs scream and the bass is solid with the ibflat.

 

Update: The pac4 ended up being the main issue. Trying to get the noise out of the system I found out the way the amp was set up that the gains were part of the issue. When I adjusted the gain it sounded better but the loc would shut down when the volume was turned up. If you pull the bass out the volume would raise a ton before cutting out.
The loc is rated at like 40watts a channel and I was trying to push over 100rms plus a sub. Next install will include a better quality loc.

For guys wanting to push a stock hu higher then normal don't buy a cheap loc as you will push past its limits pretty quick.