737-900 Elevator Trim sound

I got the 800-900 series yesterday and for awhile it had this great sound when you adjusted the trim prior to takeoff. All of a sudden, the sound disappeared. Anyone have any idea what could have happened? I checked in the PMDG sound folder in the main FS9 sound folder, and both the trim up and down sound files are there and they work when I click on them .Well, after I posted this, I found a fix. I couldn't figure out how to delete this post , so this is what I did to get the sound back. I had to select another PMDG 737 and then the trim sound worked in that aircraft. Then I reselcted the plane I had been using and now the sound is back on that one too. :)