Don’t get any humming, it’s the internal bits inside the boom clattering as the boat rocks. If I secure the boom to the coach roof grab rail it makes it worse but by allowing the boom a small amount of swing by just sheeting the main sheet in, the noise is mostly eliminated from inside the boom but is replaced by creaking in the mainsheet traveller as the boom swings with the roll. So it is the clattering of the internal components of the single line reefing system inside the boom that I am trying to cure.
We have had some very strong winds in the Ionian recently so I have 2 reefs in the main, when I leave the Anchorage in a day or so I’ll shake the reefs out and see if the movement within the boom reduces the “clattering”