Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Constant shrill fan noise

I've been very happy with several APC units purchased in the past, but this one (BX900R) is Not Acceptable due to a constant, shrill sound from the cooling fan. The fan never goes off, so the room is filled with an annoying sound at all times.It is headed for the trash.(I have two of the older APC BX1000 units, and both are air-cooled and completely quiet.)