N2details

Greetings from one ruined by Lexus. Everything else just sucks in comparison.

I have two Lexi - 2013 RX350 for the wife and I drive a 97 ES300 for work (company car). This post relates to the 97.

I apologize if I throw in too much info, but that's kinda the world I live in so here goes:

I recently replaced the factory HU in the 97 ES300 with a Kenwood KMM-BT315U. Not super nice, but all I wanted was SAT radio and IPOD controls. Bear in mind, the factory radio was working fine with no issues so all the problems I discuss below are new. Everything else was left factory (amp, speakers, sub). I got it from Crutchfield so they threw in the wiring harness and mounting kit. I got everything hooked up and all seemed well until I turned it off - crazy annoying popping sound from the speakers as the unit powered down. I also began to notice a very low humming noise all the time - almost not noticeable if music was playing. You could hear it if the sound was off or like between songs. Below is what I've done to remedy the problems and the results (or lack thereof).

1) Took all grounds back to the batt neg terminal just to make sure I wasn't trying to ground on part of the frame that wasn't actually grounded. No change in either noise.
2) Moved power to the amp from the HU to the ignition wire from the factory harness. This eliminated the continuous low humming noise but the popping sound continued.
3) Installed gound loop isolators on both RCA outputs from the HU. Took both grounds back to the batt. No change. Removed GLI's.
4) Grounded the amp chassis to the HU chassis. No change.
5) Grounded the amp chassis to the batt neg. No change.
6) Moved power to the amp from the ignition wire to the constant 12V power wire from the batt. This of course eliminated the popping sound, but only because the amp never powered down. It actually popped when I unplugged the harness to move the wire back to the ignition wire.
7) I plugged the factory HU in and verified 12V power to the amp so I don't think a converter would help. I also read that this usually only helps when the pop sound is heard when you turn ON the radio, not OFF like mine. I did not see how/if the voltage changed at turn on or turn off, only during operation - if that matters, let me know.

I really don't want to mess with a factory amp bypass unless I absolutely have to. I can't imagine it will sound better than it does with the amp since I would lose the sub. I've read in a couple places (not Lexus, but same problem) where people have installed power-on/off delays on the amp and that solved the problem. Has anyone here heard of that? How would a delay help? It seems to me there must be some sort of capacitor /resistor in the factory HU that slowly bleeds off power from the amp when you turn it off.

Any words of wisdom would be much appreciated.