I am currently active on Music Stack Exchange. I've been posting a lot of answers and questions - and a bunch of them had received unexpected downvotes, and on one of them, user45266 tells me that it was a great answer and personally would not have downvoted this. Another day, someone had commented on another one of my unreasonably downvoted posts over why it was downvoted. User45266 came and replied to the commenter that it wasn't the first time he / she have noticed my posts voted down for no reason, and that he / she suspects foul play. Can someone explain this?
I know this might be easier said that done, but: don't worry about it. Just try to be factual, respectful, and open to constructive criticism at all times. If you receive a downvote, re-read the question and current answers (including your own) and see if there's anything you can improve. As long as you do that, you're still contributing positively to this site, and that's what really matters.
Sometimes it's hard to spot the logic behind a voting pattern here. Occasionally the most basic question will pop onto the Hot Network Questions and a user will walk away with 50+ votes for their equally basic answer. Meanwhile, there are some incredibly deep and well-crafted answers that have maxed out at about 3 upvotes. Still other times I've seen an incorrect answer run away with 10+ upvotes while a factually correct answer sits there with negative votes.
And then you have the voting patterns of individual users; some users vote on everything, some users only vote on questions they take the time to answer, and I know of at least one user that averages out to one upvote and one downvote a month (!).
The fact is that there are too many factors at play, and it's not just a simple question of whether your answer is right or wrong.
If there was foul play and a user was targeting you and downvoting all of your answers, it would be flagged by the system and be reviewed by the moderator team.
I absolutely second Richard's answer as a general one, but thought I'd have a quick look at what sort of ones were getting downvotes, and there is an improvement you could make to some of them. An example being https://music.stackexchange.com/a/78641/104 - where the question is:
Do Neapolitan chords exist in modes with a minor second?
and your answer is effectively just a list of chords, as opposed to the top voted answer which, despite the lack of punctuation, provides a lot more to the reader.
So the guidance I would give is the same as Richard - if you get a down vote, see what you can improve.