I just recently noticed a problem tonight with my SWR rig. I have an SWR Bass 750 head with Goliath III and a Son of Bertha cabs. I was playing around when I noticed a high pitched hiss/crackling noise. However, this noise was periodic and would come and go. It would happen for about 2-3 minutes and then stop. A little time would go by and it would start again. This happened regardless of whether I was actually playing or the bass was sitting plugged in without me plucking the strings. I tried other basses and the same thing had happened. So, I know it's not a problem with the bass. I have the horn on both cabs up about 1/4 of the way. However, when I turned the horns off, the noise would go away. This was happening with both cabs. Is there a possibility that there is a problem with the horns on both cabs? Or could it be something with the head? I'm aware that horns do hiss, especially with treble boosted up, but this was a more noticable crackling hiss that would come and go. Any ideas? Any help and advice would be greatly appreciated. Thanks!!!