Yes, seriously earplugs.Earplugs?
Seriously though, I've had tinnitus for a while now and when I wear plugs there's less ringing in the ears that night when I'm trying to get to sleep.
The OP already stated that he has custom ear plugs... I was thinking of getting some made myself, but now I am not so sure.No one has mentioned just having your ear doctor make you a custom set of plugs for $100. Nothing will ever fit or work like a pair custom molded for your exact ear.
It may not be the bike sound that is causing you issues. Try some different helmets. I find that if they do not fit snugly around my neck the noise is greater. Take your hand and put it along the bottom of the helmet and see if that helps. You could put something in there like a wash cloth and see if the noise level goes down. Another thing you might try is a taller windscreen to cut down on the volume of air passing under the helmet.
Hope this helps.
When I took my test ride the first question I asked if it was a Termignoni exhaust and was shocked that the stock one would sound that loud. Not complaining just surprised.