checked the unit and found Blender left slide motor making grounding noise every time the slide goes up or down. talked to mfg, talked with Rodger. he recommended to replace motor because it's going bad, will obtain part and return. I deactivated left side until we fix it. 6-12-19 returned with part. removed old liner actuator and installed new actuator and checked operation by blending with unit. found no noise in unit.