Fishgut,

That humming noise is from using too much weight on the downrigger. It doesn't hurt the fishing whatsoever. It is bothersome though- isn't it? If you can't stand it anymore, change to a smaller weight. I have grown accustomed to it and it doesn't bother me anymore. However, it is kinda like living next to the train tracks. Just a matter of time...

Downriggin'
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"If you are not scratchin bottom, you ain't fishing deep enough!" -DR

Puget Sound Anglers, Gig Harbor Chapter