Frequently Asked Questions (FAQs) FAQs for Product: Fisher & Paykel Flexifit HC406 Petit Nasal Mask 1. I use this mask with a fisher and paykel HC 608 with heater tube and cannot handle the whistling it produces or the moisture build up in the mask how do i prevent this? i have also tried turning the thermostat down to no avail help!? (Posted: 15th July, 2009) Question & Answers for Product: Fisher & Paykel Flexifit HC406 Petit Nasal Mask Q. I use this mask with a fisher and paykel HC 608 with heater tube and cannot handle the whistling it produces or the moisture build up in the mask how do i prevent this? i have also tried turning the thermostat down to no avail help!? (Posted: 15th July, 2009) A. Whistling is almost always caused by excess moisture in the actual mask cavity. Reduce or eliminate this excess moisture by turning down your humidifier (usually to about level 1), or even off and just let the air flow over the water without any heat. You will also need to dry out the tube and mask in case their is some residual water in them. Only raise the level again as the night time temperatures increase. Back to Top Submit A New Question Can't Find The Answer You're Looking For? Submit Your Question Below: Related Product:  Fisher & Paykel Flexifit HC406 Petit Nasal Mask Your Question:  (Please enter One Question Only! You can ask as many questions as you like, but do not combine them into one post!) Your Reply Email Address:  Security Step:  Enter the text to the Left in the space below: [ CLOSE WINDOW ]