How to quiet down noises from inside the boom?

[JPL]

On a Bavaria 39. Suffering from very loud noises coming from inside the boom. They come and go based on wind strength and angle, it starts with a pulsating noise that gets louder and louder, with some metallic high tones. From inside a cabin you'd swear there is an engine running!
I am new on this boat so I have to find my way around this without help from past skippers. First I tried to stop the flow of wind getting inside the boom by putting on the cover for the lazy bag that goes around the mast. then I tried pulling reef lines to make sure they would not be too lose. Last I took a look inside the boom from its extremity and I see steel cables running there, so I tried to muffle the sound with a rag placed on these. No effect. I can feel the topping lift vibrate, as well as these cables inside when there is a gust of wind.
The other yachts are quiet so something's wrong here. Any clue would be appreciated.
JP

[Vasco]

Try easing the mainsheet or topping lift. The noise is usually caused by too much tension on the boom.

[Ex-Calif]

Originally Posted by JPL

On a Bavaria 39. Suffering from very loud noises coming from inside the boom. They come and go based on wind strength and angle, it starts with a pulsating noise that gets louder and louder, with some metallic high tones. From inside a cabin you'd swear there is an engine running!
I am new on this boat so I have to find my way around this without help from past skippers. First I tried to stop the flow of wind getting inside the boom by putting on the cover for the lazy bag that goes around the mast. then I tried pulling reef lines to make sure they would not be too lose. Last I took a look inside the boom from its extremity and I see steel cables running there, so I tried to muffle the sound with a rag placed on these. No effect. I can feel the topping lift vibrate, as well as these cables inside when there is a gust of wind.
The other yachts are quiet so something's wrong here. Any clue would be appreciated.
JP

Any cable under tension can resonate. The sound can actually travel from the source to many unlikely places. It may seem like the boom is the source but the source can easily be somewhere else. I would guess the common solution is to stop the vibrating cable to muffle the source. Imagine the cables on the boat are guitar strings and the boom and mast are the guitar box, the sound can travel inside the box.

If the sound persists long enough you can quickly run around the boat putting your hand on every shroud, the forestay, the backstay etc. to see if you can find the guitar string that is vibrating. If the sound is transient it may be tougher. It could also be a shroud resonating above the spreader where you cant reach it to muffle it nut not resonating below the spreader.

I would certainly make sure all the standing rigging is properly tensioned, followed by, as suggested already, loosening any running rigging that is tight but not in use, i.e. topping lifts, spare halyards etc.

You may also end up getting a rigger to ride along on the boat.

[JPL]

Thanks. Chasing noises is a tricky business... I'm taking all suggestions in consideration. Easing a bit the topping lift (can't do much with the bimini), and a bit the mainsheet has eased the noises, and changed their nature to a more acceptable sound, so there's progress
Getting a rigger on the boat is actually a very good idea as I'm sure some progress could be made in this regard.

[Waterway Guide]

We called it the "didgeri-boom"and we fixed it by taking the pressure off the mainsheet, which we had kept tight to keep the boom from swinging. Then we instead tied a line athwarts from each side of the hardtop to keep the boom stable. It was the topping lift that was actually making the noise, like a very long bass string.

[JPL]

Good idea as I have the same problem: keeping the mainsheet tight to control the boom swing, and the topping lift was vibrating so much it could be the source of all this racket.
Thanks. Maybe I'll sleep tonight

[stacy]

Agree with ex-calif, our cats mast would resonate only at a specific wind speed and wind angle and you would swear that it was the boom making the noise.

[Andrew G]

Assuming you have tracked the cause to the topping lift you can stop it completely (at any tension of main sheet etc) by wrapping say 3 turns of, for example, the main halyard around it. The principle is the same as the spirals around the top of tall steel chimneys to stop them fluttering at a resonant frequency. (I had the same issue). Andrew G.

[charliehows]

or you could make a boom cradle and let the toplift off