fr8mech wrote:As seals get older, they become a little stiffer, less pliable. The seal takes a little bit more pressure to seat against the seal depressor or frame. The hiss you're hearing is the air escaping between the seal and the frame. It should go away rather quickly as the pressure differential goes up.
For a little aside, back in the day of "smoking on aircraft" we used to hunt for pressurization leaks along seals by looking for the nicotine buildup that formed around the flaw in the seal.
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