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Halyards under tension don't seem to slap internally too badly - as a rule. I think a lot of the internal slap comes from unsecured wires - the VHF coax or aftermarket wind instruments' cable perhaps the most likely culprits.
Some have run pipe insulation foam over the wires, others have attached un-clipped zap straps (wire ties along the wire - the long ends hold the cable itself away from the mast walls. But both of these could interfere with the space needed for the internal halyard runs.... and both techniques would work best with the mast down - but then you could probably work out a more secure and permanent (and seamanlike) way to do it.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)