You have been conned. The modulator valve in on the transmission. The FM radio has a "demodulator". FM modulator? here? Fill me in - I'm old but still learning the hard way. So show me! It is possible tho that the framus coil is leaking. that's a cob too!
If you mean what I think you mean then the answer is probably yes since the modulator works with frequency from the original stereo example: 102.2 you can select the frequency I think or a preset one would be set if not. You connect the modulator to the CD changer and that's it the CD changer is connected to power and you have music.
A reason for using a FM modulator is to keep your original stereo that probably does not play mp3.