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Possible the turn signal housing is rubbing against somewhere where it is touching or mounted to the fender? Try removing the housing, see if there is any wear marks on the housing or fender (or both). Before reinstall, a light lube on the pegs that insert into the body plugs on the fender and maybe the perimeter of the lens, especially where it may contact the fender or bumper.
Without checking in person, this is my best guess.
Follow up for future searchers - after taking so many things off the front end to test, ended up being the little bracket that attaches the brush bar to the area near the sidemarker.