Unit was still doing at time of arrival. Unable to pull static pressures due to position if air handler. Tried lowering and raising fan speed. Talked with Rob and Dale about possible problems. Unable to figure out. Did online research and found info on oil being in coils from manufacturing causing similar problems. Washed could with Dawn/ water mixture and rinsed thoroughly. Doing seems to have stopped. Customer will change drop plans tonight and monitor over Friday and call us back if problem persists.