strange audio prob

Hi people, i have a strange audio prob if any one can help of who has had this prob before.

i fitted some new door speakers in my mondeo as the ford ones were shot, now if i play a cd from the multi changer ( std ford head unit ) the sound anit all that, if i fade all the speakers you can hear a diffrence:

front right= nice sound

rear right= nice sound

front left= is quieter than front right with poor bass

Rear left= is quieter than rear right with poor bass

Now if i turn the ford cd multi changer from cd over to the headunits FM radio this is what i get:

front right= nice sound
rear right= nice sound
front left= nice sound
rear left= nice sound

Now to me this sounds like the multi changer is playing up, but i thought the head unit would control the out put not the multi changer?

Any idears guys.

Ryan. :smoking: