woosh sound while braking
 

while using my brakes I noticed a large woosh sound comming from my rear
brakes. It happend twice last night, (after not having used my car for 4
days) and once this morning. Is this something I should be worried about,
as it happened and then did not happen again. My 2002 accent has 62k and
has never had the brear brakes done (front twice). But I did just have my
car inspected in April and the brakes passed... any ideas?