Fisher & Paykel SleepStyle+™ series – Ultrafine Air Filters (3 pack)

These are ?probably? supposed to be a second layer/add-on to the normal filter (the online description doesn't explain how to use them and no description on the packet) . But when you do this the machine makes an unacceptably louder running noise., as though it can't cope with sucking the air through two layers of filter material.