no engine sound

Hello, I am running Window 7 Professional and am having an issue with engine sounds in Flight Simulator 2004. When loading the default aircraft which is a Cessna 172, all sounds including engines are working properly. However when I choose any other aircraft, no engine sounds are present. I have tried multiple re-installations to no avail. All sliders are where they should be in the settings. Oddly enough, I also run FSX, and all sounds on all aircraft work properly including engines. Thank you.