I'm looking for some advice here. I drive a 2012 Altima 2.5S and during the winter months when it reaches -20C to -35C my ventilation system starts to make a fluttering sound on startup and, most of the time, then works itself out. I'm writing in, however, because it doesn't always work itself out anymore. When the temperatures get warmer, the noise goes away until either next cold spell or winter (it's been going on for a few years).
Any ideas as to what it could be?