What did Shakespeare mean by 'a pipe blown by surmises, jealousies, conjectures'?

If you look at the whole quote it becomes fairly obvious. 'Rumour is a pipe blown by surmises...' It's easy to spread rumours, because the least little thing (surmises, conjectures, petty jealousies, hints, sly looks, etc) will fuel the rumour, and the 'sound' (of the pipe, which belongs to an organ in the passage) will swell and swell until it cannot be stopped, and everyone ('the blunt monster with uncounted heads, the still-discordant wavering multitude') can 'play' it. Henry IV, Part 2.