Sunroof Vibrations

I got the car with about 28,000kms, and shortly after, I noticed that sometimes the sunroof would have a super annoying vibrating sound emanating from it. It doesn't always happen, but when it does, it's quite frustrating as it's almost right beside my right ear. Oddly, it mostly happens when I'm driving at highway speeds, but not always... Sometimes it'll go a few months without doing it, but then it'll come back randomly, and even in different times of year (sometimes in the winter when it hasn't been opened in months, and sometimes in the summer after being opened a bunch of times). There's no real pattern, and the garage can't fix what they can't see or hear.