Not sure what to try.
I installed an Autotek SS300.2, and an IDQ10.
Stock deck, used a line out converter (decent quality), sub box I made between .75 and .80 cuft. (sealed) and sits underneath rear seat (down firing).
Ground and all that crap are fine.
The issue - I wasn't happy how the sub sounded, especially while driving. It would sound pretty good/loud while sitting with truck off, but would be quiet when driving. Also most rock or high frequencies would make the sub "distort" very easily.
So I decided to run speaker wire from the amp in my Thunderbird (Autotek XS900.2) to the sub in my truck. Turned the music on in my Tbird (truck off), and the sub was hitting about 4 times harder and louder. I was hearing what I expected when I put the sub in, in the first place - loud, bass was vibrating everything, etc... and rock and every type fo music sounded great.

So, I took the amp down with me to work. Pulled out the passenger/middle front seat. Hooked the amp up real quick to see if it was the amp (the SS300.2 I thought was fried in the first place), and it sounded fantastic (truck was off). Sounded like it did when I ran the speaker wires from the Tbird to the truck.
So I installed the "new" amp, put the seat back in, and took off.
Then I realized, same crap. If I turned the volume up on the deck to where I could listen to it before (when the truck was off), it would "distort" even before that point. Actually when the truck was off, I could pretty much max out the volume (get it way up anyways), but with it running, I can get it to about half way to where I could when the truck is off.

I had always figured it was just road noise or something, until I tried the new amp, so I know road noise isn't the issue.

So, any thoughts?

 

Chances are that it is your line out converter. Those things are just plain junk, no matter who makes them. The problem you are describing is due to changes in voltage coming out of the deck. On a good quality deck you should have anywhere from 4 to 12 volts of output voltage through the RCAs, In your tbird you probably have around 4, that is the most common, resulting in sufficient input voltage into the amp. In your problem vehicle you have less, resulting in very poor sound quality and amplification, while the vehicle is running. When the vehicle is off you may have enough voltage to push the sub somewhat. Solutions: (1) quit trying to save money and cut corners and buy a real head unit. (2) Purchase another line-out converter.

 

Get a JL Audio Clean Sweep. AWESOME units. I am an audiophile nutjob myself and that is what I plan to install (already ordered it...I'm waiting on the rest of my system to arrive) in a week or so.

 

In case some got the wrong idea, The answer is to purchase a real head unit, those who claim to be "real audiophiles" know that using line out converters only decrease the s/n ratio thus providing unwanted problems and unclean sound. Same yourself the trouble, go to a reputable stereo shop and purchase a head unit, have them install it so it looks professional and put the headaches behind you, plus they assume all warrenty problems including installation issues.

 

As everyone said before, I've also run into several interesting problems, in different installations. Most of 'em dealt with the L/o coverter. It's the only piece of your puzzle that doesn't fit. Here's a few suggestions. Some l/o converters have ground wires, it is NOT always best to connect them to the truck ground. Also, Make sure your amplifier body is NOT grounded(i'm not talking about the terminal). What about the gains on your L/O converter. It could be too high(amp clipping?) or to low?!

Do you have engine noise?

 

Haha, not trying to be cheap lol. I just wanted the stock look.
The deck in the Tbird has 5volt outputs.

I know loc's pretty much suck, and that's what I was figuring/hoping it was.

I'd never buy anything local, internet is the only way to get a decent price on stuff. As far as the install, please don't assume I don't know what I am doing/can't do it. Plus, most the local shops suck. I could care less about warranty or install issues. Especially the latter, cuz if it's done right there shouldn't be any issues

I think what I'll do tonight is take the deck out of the Tbird, wire the power, ground, and ign. into my truck, and put the rca's to that deck, and go for a quick drive to make sure. If that's the case, I'll just do a real install on the deck into my truck for now, until I figure out what deck I would want for the truck.

Thanks for the advice thus far, I'll post when I find something out/confirm it tonight.

 

Nah amp isn't touching any metal, gains on loc are all the way up but amp is not clipping, no real engine noise. There is some small "feedback", as noticable when changing songs (very faint, but there).

 

Didnt mean to get on anyones bad side, I have just seen too many people on this site refer to themselves as huge audiophiles and they are using audiovox. To you Aaron T i apologize. I do agree with you that internet pricing is always best except my local shop gives me their price for equipment plus everything I buy comes with a lifetime warrenty, they find ways. There install team, who I only use when I am too busy to do it myself is excellent at producing exactly what I want. Anyway... The feedback is probably a ground loop caused by the loc, as far as any other concerns, you know whta you are doing so just double check that nothing is out of place, gains are set correctly, etc.

 

Nah it's no big deal man. It was way early in the morning for me when I replied.
I am sure you are right about it being the loc, just wanted it to stay stock looking ya know, but oh well. I'm not gonna sacrifice the subs sound quality for that, which I knew it wouldn't have been as good as a good aftermarket deck in the first place....but didn't think it would do this.
I really do appreciate all advice.

 

Said screw it and just installed the deck. Looks great in there btw

Still should adjust the amp, but sounds a lot cleaner over all. Doesn't get near as quiet while driving, so I'll assume that right now it's just road noise/exhaust, especially since once I stop, but sitll have the engine running it sounds the same, or real close.
I do think I need to remove the padding underneath the carpet that's underneath the sub, and I may add another sub now that I have the big amp in there.