I'm trying to understand a noise issue on my Yaesu FT-891. I have very high 60 hz electric buzz on most bands with 40 and 15M being the worse at about S9+. My antenna is a MyAntennas 66ft EFHW fed with 25 feet of RG-8X coax. I've noticed that if I unscrew the coax shield to the antenna input of the 891 and just leave the center feed connected the buzz goes away completely. Yet, if I screw the shield back on the noise is there.
It's a bit perplexing - the assumption being that the coax shield is capturing the noise. But, why wouldn't the noise still be there if the shield isn't attached. It implies the endfed wire is not picking up the noise and the shield is. I would think the some of center wire of the coax and the wire antenna would still have the noise if the shield isn't connected. Note that chokes, ferrites, grounds make no difference.
What are thoughts on this? What am I missing here? Why would the buzz go away completely when the PL-259 shield is unscrewed ?
PS - I've shut down power from the fuse box in my shack room and around it as well and no difference (running the rig on battery).