Velodyne SPL-800i

Recently picked up a Velodyne spl-800i and it’s been running fine under testing. Decided to plug it in tonight and watch a film but noticed if the volume is very low the sub has a slight crackle and cuts in and out. If the volume is higher the sub works as expected and it can be turned right up without any issues.

I have read posts of issues at normal or high volumes but can’t seem to find issues at low volumes. I will pull the amp panel off tomorrow to have a look if it’s anything obvious but has anyone else encountered anything similar?