I'm using an Invacare Platinum 10 10 lpm concentrator at 8 lpm. It's far from my first experience with a 10 lpm concentrator, but it is my first time using Invacare and also my first time using a humidifier bottle (which my nose loves). The issue is that it "squeals" very briefly two or three times a day and some of those squeals are followed by a lack of air flow. The air flow sometimes resumes after a few seconds and sometimes I have to toggle the machine off and on to restart the air flow. The squeal is very similar to the noise it makes - also very briefly - when the unit is toggled on. The supplier is responsive but as baffled as I am about the cause, so they swap in a new concentrator. We both now think it's associated with the humidifier and specifically with the tubing that brings oxygenated air into the water bottle -- maybe it has to be a very tight connection? I'm wondering whether anybody else has had a similar issue and if so whether they can suggest a fix. Thanks so much.