Came out to perform preventative maintenance on AC/Heat pump. Customer met me outside home. We went over maintenance needed, discussed how system was doing, and how the holidays were for them. Customer stated that the system was making a rumbling noise, and that it only happened every so often. Customer also needed a filter, so I changed it. Inspected blower assembly, motor, coil, drains, electrical components, heating elements and overall condition of equipment. Washed condenser coil. Checked thermostat operation, wiring, compressor, fan motor, capacitor, amps, temperatures and pressures. Cycled unit in emergency heat, and heat pump. Found no noise issue during maintenance, but did explain that the new blower motor we installed does make a low rumble noise when shutting off, but that it’s normal. Customer said that she believes that could be it after I described the noise. System is operating properly within manufacturing specs at this time.