Be careful with what you do to get rid of the hum. I remember a big monohull that had a "hum". The owner went out and applied "common sense" and the hum went away. The problem was we were instrumented, after the owner applied common sense we couldn't go fast enough to hum anymore.

Starting with easy.

Check the leading and trailing edge. They should be smooth, no bumps or humps. Check the foil specs to see if the trailing edge is blunt or square edge, there is a difference. Also check the foil specs to see what thickness the trailing edge should be. It is normally 1/16" to 1/8" or a % of the foil thickness.

Check the foils for stiffness. The stiffer the foil the higher the resonance frequency. If the foils that hum are noticeably less stiff than the foils that don't hum that could be your problem.

Look for local delaminating. A local delamination will vibrate.

Make sure it is not the housing that is vibrating. Tighten the bolts on your rudder assembly and stuff some foam between your rudder and dagger board well. Swap rudders and dagger boards side to side.

Check your dagger board well to see its loose, tighten and check your gudgeons, check your transom.

Look inside your boat. If the problem is only with one hull you might be like me and find that drill bit you lost.

Carl