The chimes are embedded in the software from the audio processor. They come through the front left channel, and your reverse sensors will emitt beeps from the correlating side of where the obstacle is through the rear channels. The only way to get rid of them is do what DFW_Muscle did and get one of the audio processors available that can adjust the chime volume independently.
HOWEVER, you will need to get aftermarket amplifiers and new speakers as well, because these processors are designed to bypass the factory amplifier system. You cannot just get the processor and be done. They make your factory amplifier useless. So beyond the $300 or so for the processor alone, you'd be spending much more money for an amp, new speakers, and hardware/wiring, along with labor if you have someone do it. All in you'd be looking at well over $1000 just to get rid of your chimes. Your stereo system will definitely sound much better though
Welcome to modern vehicle integrated control operations. Where quite literally, your turn signal and sub woofer is integrated.