Nigel - first of all brilliant video. I find it hard to believe that is your second vid!
Now about Bitchin Betty
I think your using FSX but this might help find the offending sound.wav. On my FS9 system the folder C:\Program Files\Microsoft Games\Flight Simulator 9\Sound\GPWS has the file "WhoopWhoopPullup.wav" along with all the other GPWS sound files. You could rename it temporarily and record a silent file using the original file name. I would say delete it, but that may mess other more modern aircraft that use it and also might cause an error.
There may be other locations also - there are quite a few versions of that GPWS gauge around and a search might reveal other locatons. I am being lazy and can't be bothered looking for them right now!
Oh, one nit pick - couldn't you find a British artist to perform the music instead of Frankie? ;-)
Nigel²
PS. Just noticed this entry in the "Sound.ini" file in that folder "Sound22=./Sound/GPWS/WhoopWhoopPullup.wav,95" If I remember correctly (always a dicey proposition) if you change that 95 to 0 it should silence the sound. This leads me to believe the example above is a new version of the gauge because I don't think the older versions had that file. If you do have an older version, check the panel.cfg (if you have FSPanel use that. The SOUND gauge will be invisible but will show as a small square in FSPanel Studio) so either delete the line in panel.cfg or comment it out. The display for the GPWS unit may be visable and that could also be deleted if you want.
Just did that search I was too lazy to do and found whoop sounds in some folders in addition to the location above. On my setup,the sound folder root has a "whoop.wav" sound and the Project Folker sound folder also has some. I think those older versions of GPWS used either FSSound.dll or
GaugeSound.dll to produce the sound, the newer GPWS version does not use those .dll files.
OK enough, Top Gear is on BBC America so I am off.