Where is the factory cd changer in the 2004 BMW 325i installed

l did not bother getting one in my 2004 325xi but if l recall correctly there was one unit that would fit in the glove box & shuffle something like six disks or u could get a larger unit which fits in the back drivers side of trunk which l believe is where my Nav DVD is. If u have the Navigation system, & only a single CD player like mine, then u push the button on the upper right corner of the Nav panel & it will flip up & allow u to insert a disk & close itself after it sucks the disk in.

If the car comes equipped with one, then it is at the left side of the trunk.
There is no such thing as one being installed in the glove box.
The Germans are smarter than that.

Paul is correct. A Nakamichi changer was available for installation inside the glove box.
If ordered with Nav this is where the changer went but without it could be installed in the trunk or glovebox. The trunk changer is an Alpine unit and both were 6 CD changers.

left side of the trunk