Audio Systems: Aftermarket head + factory amp = whine, chrysler sebring convertible, blaupunkt los angeles mp74

Question
Ernesto:

I replaced the head unit in my wife's '97 Chrysler Sebring Convertible
JXI, which came with the Infinity system, amp under the passenger set.

Main reason was to get wired auxilary inputs for an iPod and Sirius Satellite
radio. The new radio is a Blaupunkt Los Angeles MP74, and it runs through
the factory amp just like the original head unit.

The new stereo sounds (generally) better than the original on the high
end especially, but I get a low-level alternator whine between about
1500-2500 RPMs that is not heard with the original stereo. It seems to be the
amp, as when I turn off the internal amp in the head unit, I still get the whine.

It's not loud: normal radio volume will cover it, but it's annoying when driving
with the radio volume lower.

I tried playing with the grounds, running a wire from the radio to the
amp ground wire at the amp plug: no diference (though the original ground
wire was not disconnected). I ran the ground wire from the radio straight to
the chassis: no difference.

What don't get is that the original radio doesn't have the problem, only
the aftermarket, even though the wiring is essentially the same.

Should I try to continue tracing, or just remove the amp and run off the
Blaupunkt only? I heard that the Infinity amp has the speaker
crossovers built in, so I am slightly reluctant to do it, but I guess it wouldn't
be that big a deal.

The Infinity amp has "top down equilization," though that's not a huge
deal. I'd rather not cut wires, as I want to be able to some day put the
original system back in, but no bypass wire seems available, so I uess I'm
stuck that way. Finally, any idea on which has more power: the factory Ifinity
amp or the amp built into the Blaupunkt?

Any thoughts or ideas?  

Answer
yes that problems happends allthe time the output of your new radio is about 30 to 40 watts rms
the infinity radio only about 3 to 6 watts that is what the infinity amplifier needs to have a good sound
the input now is to high and that is the reason of the noise  if you use the rca jacks from the radio the noise will disapear but the valume will be very low

and removing the amplfier is not a good idea  you will lose the sub output

this is what you need to solve your problem

http://www.oemautosound.com/pc-216-125-radio-replacement-interface.aspx