We're considering a Series 7 for new construction. The unit would be installed in a utility closet in the living area, so noise is a major concern. The dealer set-up a test unit to make sure it won't be too loud. In testing, the unit makes two notable sounds: an almost inaudiable"purring" sound and a high pitch "electronic" sound. The purring sound is not a problem, but the high pitch sound is almost like fingernails to a chalk board. This high pitch sound isn't mechanical, its electronic (but I'm not sure how else to desribe it.) Interestingly, the dealer himself could not hear it but his installer and I could. He is now reaching out to other customers to see if we can listen to thier Series 7 units to hear if we can pick-up on the same noise. We're trying to figure out if its a problem with the specific unit or the Series 7 in general. Does anyone here have any experience with this sound? As long as you can hear high pitched noises, you wouldn't have any problem hearing this sound. In other words, you'd know it if your unit is making it (and you didn't spend your youth with your walkman turned up to 11).