Sometimes they will use their horn to alert peds walking they are passing - which is like, a car horn, because they need that for roads. I've never been "horned" but I've heard it and its not pleasant. Other times they just blow right by no warning.
And unlike walkers or bikers, I almost never see them coming back the other way. I think what has happened is they discovered the path is a quick cut-through to roads they want to get to on the other side.
Last time I was out I saw a literal motorcycle on the path. It wasn't a big one, but no doubt, it was a straight up gas-spewing motorcycle, no question about it. I had to laugh in between choking on its fumes.
I'm used to getting buzzed by cyclists but this is a bit much, and I've been walking less in the worse-affected park. Another park I walk in is a national park and the rangers don't tolerate that kind of crap. But the state and local parks don't have the manpower to enforce.