Whoosing sound from membranes? (PISA)

Owl2011

When you are using your PISA do you hear a whoosing sound from the little white flaps (membranes)?  Sometimes I do, but most of the time I don't.  When I do, I'll normally stop and push it around until the whoosing stops.  But, does it really matter?

blondde1104

You may need to replace the membranes.  I heard you need to do so every 3 months.