So i was under my hood revving the engine a bit when I noticed after revving, when engine decelerates I hear a knock type noise around 2000-2500rpm before the engine returns to idle. Its quite faint you can really only hear it when the hood is open but it is definitely there. Any thoughts? I think its coming from the lower end not sure though.

1994 Honda Prelude Si all stock 193,000 miles, I got it at 165,000 miles, as far as I know there has been no work done on the lower end.