Well...
...I'm making a bit of a guess...
But I would have thought you have nothing to lose by putting a selected, suitable FSX Sound Folder in the selected FS 2004 Aircraft Folder.
Just re-name the existing sound folder for safety.
After all, they are just simple .wav files!
Give it a try...

...!
Paul...sounding off... 8-)...!
...blame my Mate if it doesn't work...

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...!
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.