speaker buzzing with engine

As my RPM's go up when i drive it buzzes up with them, It isnt my Subs its the rear speakers. How would I get that to stop, and why is it happening...

you have an induced engine noise ..... how are the speakers in your car powered (which have a seperate amp and which use the CD players' built in amp)

make sure your power wires are not ran by the rca s