Yes, it is completely normal. It is the engine/trans shifting due to the lessening speed, and the vibration is transferred throughout the chassis. Mine was horrible from 25mph down to 10mph or so. It didn't help that the cold weather last winter made the ZZP Poly mount as hard as a rock. I passed the Poly mount over to someone down south and went back to the OEM mount twisted 90*. I did, however, buy a spare OEM mount in which I'll install the MSP bushing in the warmer weather. The cold really made the stiffer mount unbearable.