I have a loud hissing noise in my PMDG 744. Its there all the time. In a Cold/Dark cockpit. Outside the aircraft and even when I push the "Alt" keyboard key its still there. No sound Volumes seem to change it.Thanks,Andy

. . . . look for high-pressure airline leaks - particulary couplers.. Check the nosewheel/s for leaks. .

Have a good look round the cokpit for reptiles would be my answer.Ok, options are, update the soundcard drivers and if using on board sound buy a good soundcard you should see a big difference.Is it only the 744 that does this?Try switching traffic off in the options window, you may have an aircraft near you??Try changing airports and see if the same happens??And now I am out of ideas!!Sorry for the first line, could'nt help it.Daniel

Its not anything serious its your cockpit fan! Simply turn it off in the OVD panel!Hope this helps! :)