Upon arrival I tried recreating noise by shifting reversing. The homeowner said the hissing noise at the start of the shift was the noise but really loud and did not stop till he shutdown system. I checked refrigerant pressures in cool and heat. Valve shifted normal every time. It must of stuck once from lack of shifting during the cooling months. We discussed quotes that was given to him for new system. I could not pun point a problem at this time.