I have a new 2018 Landmark 365 Newport with disc brakes. When parked and no braking is being applied from the tow vehicle, the Dexter Electrically Controlled Hydraulic Brake Activation device make a surging sound. I sounds like it is trying to pump intermittently. The trailer brakes work fine but seem to have a slight lag. I am thinking the lines have air in them and need to be bled? Has anyone experienced this?