Weird Radio Problem 2001

I have a 2001 Malibu and when i have the radio on the radio works fine while driving, but when i slow down or come to a stop the radio gets lower and them when i speed up it gets louder. Is it defective or is this how the Malibu radios work. Or is this just a weird situation???
Thanks
Kevin

That's the speed compensated volume knob. It is the outside knob on the volume control. To turn it off, tunr it counter clockwise until it is at its lowest volume.