Slight twist on door speaker install but help needed

[Ttownthomas]

I'm in the midst of an audio upgrade (stock 87 930) where I am trying to keep a Stock appearance other than a small removable sub box in back footwell (sub not done yet.) I wanted an external amp to drive 4 full range drivers plus a sub. The stock appearance is the hard part. I also did not want to drill or cut the door cards or sheet metal.

After some trial and error I determined that I could mount the 5.25 inch focal speakers under the door card. I also wanted to mount them firmly to the door because the plastic floating cup has sonic issues. This presents a problem seen in other posts where mounting the speakers to the door uses up your screw holes and the grilles have to be glued on.

Instead of custom making mdf spacers I found an eBay listing for speaker rings and asked the seller to make me a set with internal 4.5 inch diameter and external 6.5 inch diameter. That allowed me to straddle the 5.5 inch hole in the door and use the exsting door card hole.

I pre drilled holes for the following:

Through bolts to hold speaker ring to the door (already installed screw heads shown)
Holes for mounting the speakers (already done see photo. Rotated out of the way for grille install and because they don't line up with the grill exactly anyway)
Holes for mounting the grilles (small holes at 45 degrees)
Larger holes to accommodate the screws that stick out the back of the door card (the ones that held the old speaker cup on)(larger holes at 90 degrees)

Here it is

Here is with the door card installed

Now simply screw the speaker cover through the door card and into the mdf pre drilled holes

In order to keep a stock appearance I bought an adapter off eBay that plugs into the rear if my factory Reno head unit and gives me pre-amp outs and a remote turn in wire. So I have a Reno head unit hooked up to a modern amp under the seat.

So. On to my problem.

The amp is mounted under the passenger seat and grounded to the body (after sanding off the paint) to one of the unused 6mm bolt holes in the Foor pan. It s a JL XD 700/5.

The problem happens at turn off. When I turn off the radio from the knob on the Reno or if I turn off the ignition I get a loud popping noise through the speakers.

I tested in the following ways:

Remove pre-amps and turn off stereo (no popping)
Plug in pre amps and manually remove remote turn on wire with ignition off. Turn on stereo and then "touch" amp remote turn on wire to amp turn on wire location. (Essentially I'm turning n and off the amp manually). This also stops the popping.

My very amateur guess is that the head unit is sending some noise through the pre-amps when I turn it off and the amp still has power for a second that amplifies the noise just before it powers down.

Any thoughts?

[Ttownthomas]

I'm nearly 100% sure the popping noise is coming from the pre-outs on the Reno. I did a bunch of tests isolating different issues. Re-wired the power turn on wire to the cigarette lighter, also hooked up my iphone to rca's, tested it every witch way. Not only does the Reno make the popping noise but it has a low level hiss That disappeared when the iPod was hooked up. Darn. Frustrated. I wanted to keep the head unit.