Sounds like air in the system, at least on my Apple tablet.
Having said that, my motor failed . Noise first, followed by electric arcing. BendPac doesn’t sell the motor separately, nor do most of their imported competitors, as far as I can tell. Even the big boy commercial units have pricing structured such that a power pack doesn’t cost that much more than a motor. The motors all have proprietary spline drives, so an off the shelf motor won’t be easy to adapt.
I bough an SPX power pack to replace the original BendPac Chinese powerpack. All is well, although it wasn’t exactly inexpensive.
Hopefully, your issue is just air, which a good bleeding should fix.