if was due to a less than functional GB setting, and that was usually a direct result of using an accessory coil.
The Malan clan, in Ogden, Utah, have at least 4 or 5 of the 'original' Silver Sabre's that they have been using since '85 & '86. All with the standard 7" coil. In the past I have had three of them at one time to clean and tighten up and check out. I wanted to 'experiment' with one because I thought the coil might be bad. It wasn't, the particular unit was just out of balance for that particular coil. I swapped the coils around between them and noted variances between the settings with each coil.
Working a Passport in Time project with the Forest Service in 1992 one of the club members bought a 7" concentric coil from me because the stock 8" was too big for the brush and trash, and the hole was a hindrance.
I checked the Silver Sabre II with the stock 8" coil and all was working fine. I mounted the 7" concentric coil for her and checked it out. Noisy, noisy, noisy over some of the dirt and small rocks.
Checking the GB setting, it was quite obvious that the GB was now very negative. Bad coil? Nope, because I checked her unit using the 7" concentric coil off my Bandido and it was closer to functional, but still slightly negatively balanced.
Solution, I just found the worst ground at the site, 'Power Balanced' her Silver Sabre II with the 7" coil and everything worked great! Good, silent operation.
Now, if you're using your units anywhere near an interfering power source, then the cause might be outside RF interference. If not, check the GB setting.
Monte
MonteVB@comcast.net