Maxima radio/engine sound

[ANNASDAD]

I have a '96 Maxima with a 5 speed transmission. Recently I had an aftermarket satellite/AM/FM radio fitted to replace the Bose unit. The new radio mated to the Bose hardware, so the speakers, power amp, etc. are all still the factory Bose elements. The problem is that I can hear the revs of the engine through then stereo speakers when I’m trying to listen to the radio. The louder I turn up the radio, the louder the sound of the whir of the engine in the speakers. If I turn the radio off, no more engine sounds. I’d appreciate any insights. In the old days, it seems like there were high capacity, or high resistance fuses one could use to address this kind of problem.