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Discussion Starter #1
I bought a 2007 FJ Cruiser this year, that I love, but immediately wanted to upgrade the stereo.

I have an aftermarket head unit (Kenwood DNX6160), Polk MM6501 speakers in the doors with the tweeters mounted in the dash, and a Polk 250.2 amp driving the speakers and tweets.
Any original speakers (ex. rear pillars) are driven off the head unit.

I had the head unit installed prior to the Polk installation, and everything was fine then. I had all the Polk components installed...they sound fantastic, but there is a constant hiss coming from the tweeters. The volume of the hiss never changes, so if I have loud music playing I barely hear it. However, due to the fact that it's abnormally loud, under normal conditions it's driving me insane.

Any ideas/suggestions? I'm not an audio expert and I didn't install everything myself, so I can't supply a ton of detail. The place that installed the components doesn't know what the cause is, although they said they tried installing filters to no avail. I'm thinking about installing a sub and bridging the amp to drive the sub...then I can trying powering the speakers off the head unit as a test to see if the hiss is there.

In any case, I have to solve the issue because I feel bad for anyone riding in my FJ having to hear tweeter hiss the entire time.
 

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My guess would be a bad ground on the amp, but do you have any stock speakers or anything else that you can plug into the stock tweeter location and see if those hiss too? I doubt it's the tweeters if both of them are doing it, but it'd be good to rule them out.
Is there any hiss coming out of the rear stock speakers? I'm guessing not, so that probably rules out the head unit and it's signal. Chances are that it's a problem in the amp, or the RCA cables to the amp. Try jiggling (technical term) the RCA cables where they go into the amp, or rotating or unplugging and replugging them. If that does nothing, see if you can find where the shop attached the ground cable to the chassis. While everything is off (no power), take out the bolt holding it to the chassis, clean or scrape the bolt and whatever it mounts to so that some bare metal is exposed. Reattach the ground and make sure it's tight. That's all I can think of...
 

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Oh, I forgot- If your amp has a built-in crossover, adjust it a little one way or another and see if this helps. I had to do this to mine recently. I guess over time, the adjustment knob got something in there because I pretty much just touched it and I got rid of the hum I had in my subwoofer. I realize your Polks have their own crossovers, so I don't even know if you're using the amp's crossover, but the stereo shop may have it set up that way. Just something else to fiddle with.
 

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Discussion Starter #4
My guess would be a bad ground on the amp, but do you have any stock speakers or anything else that you can plug into the stock tweeter location and see if those hiss too? I doubt it's the tweeters if both of them are doing it, but it'd be good to rule them out.
Is there any hiss coming out of the rear stock speakers? I'm guessing not, so that probably rules out the head unit and it's signal. Chances are that it's a problem in the amp, or the RCA cables to the amp. Try jiggling (technical term) the RCA cables where they go into the amp, or rotating or unplugging and replugging them. If that does nothing, see if you can find where the shop attached the ground cable to the chassis. While everything is off (no power), take out the bolt holding it to the chassis, clean or scrape the bolt and whatever it mounts to so that some bare metal is exposed. Reattach the ground and make sure it's tight. That's all I can think of...
Thanks...I'll see what I can figure out. The rear stock speakers aren't hissing, they're easy to hear before the amp warms up and the front speakers start producing sound.
I do have the stock speakers still, so I can try to hook those back up and see how it goes. One way or another, I have to fix it because it's going to drive me over the deep end, so to speak.
 

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Discussion Starter #5
For the record, it turned out my amp was bad. One of my door speakers was bad as well, so I had everything yanked out and new components put in (and added a small 8" subwoofer).

I hopped over to JL Audio C2-650s and a small 4 channel JL amp. The small JL sub fits entirely over the wheel well area in the back. No more hiss and it sounds great.
 

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I love jl subs. Good to hear you got it taken care of.
 

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Hey since you got to try both which sound better, the JL's or the Polks?
 
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