Comments please on the following!

At certain camera angles on each axis, there will be an audible hum signifying some BG frame resonance. Apparently the notch filter function in the latest 32 bit 3 axis firmware will enable the user to dial out the associated frequencies. To determine which frequencies need to be dialed out, an acoustic spectrum analyser can be used. Here is one for MS Operation systems: search for SpecAn_3v5.exe.
For MAC here is another c/w the instructional video specific to BaseCAM BGC firmware.