There is speed sensitive volume on our cars... The circuitry is built in to the amplifier, not the radio... Infinity should be able to verify this for us.... When I first changed out my OEM CD player for the Blaupunkt, I still had the slight volume up/down based on RPM's and speed.... Also, to my knowledge, the speed sensitive volume circuit also compensates/adjusts the amplifiers internal equalizer as well....

Hope this helps...