Are you talking about the coax connecting the rig to the amp? or the antenna feedline from the amp?
A sloper excites the mast and everything connected to the mast. It is a terrible antenna for common mode RFI problems.
You can try a feedline isolator, but everything connected to the tower that supports the sloper is part of the radiating system. If you have a "half-sloper" there is at least as much current in the tower or mast as is in the sloper itself. This means the other feedlines, rotor cables, control wires and tower itself all conduct common mode.
It is unlikely a feedline choke would cure the problem, but of course you have nothing to lose and it might help. Install it at the house entrance.
You might consider a different antenna that is less susceptible to RFI problems. Otherwise work on bonding and grounding of all cables and the mast or tower.