joerg77 wrote on Jan 28^th, 2012 at 9:38am:

...thanks for that infos  :) I don't want to risk my membership - and it's so easy, it took about 5min, so if anyone want to reduce any sound of any installed aircraft: - You need an audio-editor, for example "audacity" is very good and for free. (I'm not allowed to post links, so please google it) - Open the wave-soundfile you want to edit, e.g.  your flighsim-directory\Captain_Sim\767\sound\apu_start.wav - Select the whole sound and raise volume with a negative number of decibel., e.g. -20 - Save it and replace the original audio-file, don't forget the backup-copy. Joerg

You can also use creative "wavestudio" except lower the value to 20%. The sound level is great now.