My thoughts are that all of you that experience this wiggle are ex Bell pilots.
I have never had the problem, nor have my students.
Around all helicopters close to the ground there will be patterns of air flow that are random due to a multiplicity of reasons. These air flow patterns will effect the tail and main rotors and as pilots you are trained and practiced in hovering. May I suggest more hovering practice with a relaxed and alert brain!
Coanda effects and the like are possible reasons. Some tail booms have strakes, some have had strakes and have had them removed, some do not have strakes. I think strakes were/are fitted for other reasons.