Hello. Last fall a reputable outfit replaced my old system with a: 355CAV042060, 186BNA018000, CNPVP2417ATA, and SYSTXBBUID01-C. The unit is in a room adjacent to the living room with a return pulling air from the living room. So I expect to, and can, hear the system operating. During the heating season I found it reasonably quiet (ran on low 99.99% of the time and medium only occasionally) and the blower fan made no strange noises. During this first cooling season, however, the blower fan has been making some annoying noises. I wanted to ask about this in a forum before calling the contractor.

When the air conditioner is running it sounds as though the blower fan RPM is frequently being changed by modest amounts. It sounds as though at some RPMs the fan produces a whine, at other RPMs the fan produces an oscillating "warbling" sound. Neither the whining nor warbling is very loud. However, they are clearly heard and as the fan RPM moves around the whining comes and goes, sometimes changing in pitch, and the warbling comes and goes. Which creates a constantly changing series of noises that is disruptive to quiet work, trying to take a nap, watching a quiet movie, those sorts of things. That is typical behavior especially on hot days. Occasionally, though, the whine/warble don't occur or at least aren't obvious. Unfortunately, such was the case during my summer checkout appointment. During which it was suggested I give a different config (constant low fan, efficiency, higher humidity) a try for a while. I thought the system was noisier after that (and also less comfortable) so I put it back to the original config (auto fan, comfort, default humidity) for now.

Does this noise I'm describing sound like something any of you have run into before? I'm not sure if there is anything I can do in terms of gathering more information before calling the contractor. If there is, though, I'd like to since this is a somewhat variable problem and often those aren't much fun to track down.

Thanks for your time.