Start by welding up the decibel leak, then go to a more reasonable tire.
I know a lot of you like the really gnarly looking tires but considering that rear wheel spin is not a problem on TWs,
Why cause yourself the problem. You have to unweight the rear wheel to get it to spin even in sand.
The tire it comes with is a very good match for the bike and there are aftermarket tires that may be a bit better without
going to this extreme. If you are gearing down so much that the tiny engine can torque the tire to slip you are losing enough
top speed you might as well be riding a Rokon.
Rokons use goddawefull tires and actually make them work if you like life at 28 mph.
BTW my suggestion for the weld job would be to cut out the dimple and weld on a patch so as to not impede exhaust flow.