Tyrion wrote on Jun 12^th, 2009 at 3:01pm:

Well, I tried again today. Very surprising result when I tried with the Cold and dark saved flight: cockpit sounds worked!! not surprising however, APU sound keeps playing when APU is switched of... I then tried again with a free flight startup, no cockpit sounds at all!! I'll wait and see if this gets resolved in any way... Tyrion

For me the solution posted here worked: http://www.captainsim.org/yabb2/YaBB.pl?num=1242905995/0