Came out to call for a system making a noise. Customer said that the unit was working properly, but had work done on his gas line recently and the unit seemed to be making a different noise when coming on. I checked system over and found unit operating properly. Checked gas pressure, amps, and temperatures. Only noise I hear was the blower ramping down when the thermostat satisfies, which is normal. Checked for carbon monoxide for customer as well, and had 0 ppm on my meter. System is heating properly.