Bass thump sound with each click in volume

So I just installed a new Kenwood Excelon KMM X705. It's running factory speakers in my 2016 HR-V (no factory amp) with a mono Kicker amp powering a sub.

When I adjust the volume, I can hear a slight thud sound from the sub. As if the head unit is beeping with each click, but it's bass. I can't find a setting to turn this noise off, so I'm wondering if it's not intentional.

Any ideas?