We have a Trane 2-year old heat pump. When operating in heat mode in 35-40 degree weather it makes this very loud banging noise as the external unit is shutting down. We've had installer out several times and they say this is normal. It does not happen every cycle, but often enough to disrupt our sleep and that of our neighbors who are getting very irritated. The unit is right outside the Master Bedroom and across from our neighbors bedrooms. The unit produces heat, but the noise is very disruptive and can't be good for the unit. A Techinician today suggesting installing an external thermostat that would force the outside heat pump too shut off before it hits 40 degrees and hopefully stop the heat pump from kicking into high gear. This will initiate the emergency heat to keep the home warm in cool temps... but doesn't this defeat the purpose of installing a heat pump in the first place?? The emergency heating system is designed to kick in IF there is a failure in the heat pump and not mormal operating mode, and obviously much more expensive to run. Any ideas what may be causing this loud banging noise and what is the remedy? Help! Help! We'd all like to get some sleep.

Most installer and myself usually try our best to put the outside units (heatpump or whatever) as far from the bedroom as possible,be it the home owner or the neighbors
Some units do seem to make the noise you are speaking about doesn`t matter what the brand. It seem to happen when they are switching from heat mode to defrost cycle,or back to heat after defrost, which happen every 30 or 60 minutes, in most cases, the reversing valve in most/or some cases the origin of the noise,, what to do about it, has been a even bigger problem,, lets see if any other techs can come in and help us both out with this problem