Furnace start up. Cycled system. Checked electrical connections and clamps. Found exhaust venting clamp was incorrectly installed. Removed and correctly installed. Checked venting, ok. Preformed gas leak search, no leaks found. Checked and adjusted gas pressures to maximize efficiency. Inlet and outlet pressures were checked and adjusted. Preformed combustion test. Normal levels found in exhaust. No CO found in airstream. Customer stated that the system sounded louder. And they were having duct noises. Found filter clogged. Removed and noise reduced. Replaced thermostat with correct thermostat. System operating normal at this time. Job complete.