I did a search... read some posts... tried mentioned fixes... still have the problem. And its a problem I have read in more then one post across the net.

2005 MCS with the regular factory HU. I replaced all four speakers with MB Quart Q-series speakers. Stereo sounds much better. Then a couple of days ago I decided it was time to install the amp for the rear speakers. So I installed one of my favorite old school amps the PG M25. Man it sounds killer. That was until I started the car up and "BAMMM" ignition noise... that wonderful hummmm and buzzzz and when you hit the brakes you get to hear a click...

I have RCA jacks going to the amp.

With the key on and the amp hooked up no issues.
With the car started and stereo off you get the noise.
With the car started and the stereo on you get the same noise.

With the car running or off.. I can take one RCA jack off and the noise goes away. Plug it back in and you get noise.

I checked my ground cable and even added a second line on bare metal. Still the noise. But if I take the ground off it amplifies very loud. Is it still a bad ground? Not from the amp... the amps case and ground cable coming from the amp are grounded like they should be.

I then tried an isolated power source with floating ground... nada.. noise still there.. I tried isolated power source with ground going to the amp and cars body... still noise

I checked all the speaker wires, power cable, etc... so that they did not cross and cause in inductive circuit which could create noise. Nope everything is good and I still have the whine...

All speaker cables are good and connected properly.

I then installed the amp but kept the amp itself outside of the car... yepp.. still noise.

So I took that amp out and installed a second amp. Everything is exactly as it was with the first amp... whining... wheezing... buzzz... etc....

Now if I install two amps.. one for each side... then everything works, sounds good... and zero noise... I dont plan on two amps... and I would have to buy two 1 channel amps

So Im tired of taking stuff apart and trying to troubleshot this issue. Im open for advice.