In a comment on this question I voted (with four others) to put on hold, the OP tagged me and asked, "@Travis: What do you think is wrong with this question?", notwithstanding that the on-hold message indicates exactly the reason for my vote.
About two hours later, the same user commented on one of my replies to an unrelated question: "What do you think is wrong with this question? : math.stackexchange.com/questions/959181/…" (Since I began composing this note a moderator has found and replied to the first note, and the second has been deleted.)
Roughly around this time, two of my own questions---which are both a few weeks old and related neither to the above questions nor to each other---received their first downvotes, which together with the above suggests some kind of retaliatory action might be at play here.
If this is indeed retaliatory, surely this is an appropriate use of the voting mechanic, not least because it worsens the site's signal-noise ratio. Is there any action I should take beyond pointing out this situation here?