I'm a builder and a noise freak. After my system was installed I noticed, when the house was quite in the evenings, a constant droning noise coming from the floor registers on one side of the house. After several attempts at trouble shooting the source of the noise I discovered quite by accident that the noise I was hearing was being transmitted by the water lines. I have a package unit installed in the crawlspace under my house and had requested the installers to tie the final connection hoses up to the ceiling of the crawl to keep the floor area clear for storage and access to the well tanks. The configuration of my bore holes, pipe to house and pipe to pump pack required about 30' of hose and everyplace that hose touched one of my ducts the pump motor vibration was transferred and transmitted into the ducts! The fix was simply to loosen the straps on the hose and allow it to clear the ducts. Noise gone!