So, after my initial issues with the PAC TATO unit and stock amp, I ditched any and all trace of stock equipment in my Lexus IS300.
I am now running an Alpine INA-W910 head unit, Clarion APX400.4 driving Hertz component speakers, and an Alpine MRX-M100 driving 2 x 10" Type R subs. I got everything hooked up, dialed in, and it sounded great.. until I started the car. With the engine running I get a beautiful sounding alternator whine when the volume is turned down.
Before I explain everything I have tried to remedy the issue, the unusual part of my problem is that it only happens when I connect 2 sets of RCAs (front and rear channels) from the HU to the Clarion amp.
If I run a single RCA cable to the front input and set the amps rear channel to use the front input, there is no whine.
I have tried both RCA cables, one at a time (in both front and rear channels on the HU and amp): no whine as long as only one set is hooked up regardless of which input/output used.
Leave both cables connected to amp but remove one set from head unit: no whine.
Different RCA cables / routing: whine.
Moved the ground on both the HU and amp: whine.
HU+ connected direct to battery: whine.
Jumper cables from battery ground to numerous locations on the chassis: whine.
Ground the RCA shields: whine.
At this point I don't know what else to try. I really want to separate the front and rear channels so I can use time correction. I am hesitant to use ground loop isolators, but am willing to try anything that isn't going to break the bank.
If anyone has any further suggestions, or knows where I can find decent quality ground loop isolators locally, please let me know.