Unit was making whistling noise through the return grill when the system was on. Lowered return hatch and the noise stopped. Homeowner had a filter in the air handler above the garage but not one in the return. Took air filter out of air handler and the noise stopped. Suggested that the homeowner use one only on the return indoors. 12x24x1. Drain line shut down system while I was here. Cleared drain line with water hose and ez tee adapter. Unit is functioning properly