Well, my BFG M/T have been getting louder and louder over the last year, to the point that they are unbearable at 100km/h. But instead of new tyres I decided to install some sound proofing (or deadening) in the cab. I can't justify the $$$ for dynamat, so instead I went the getto option and used bitumen flashing from Bunnings
For $100 I got enough to cover the rear wall, side walls and doors (plus a bit left over).
I know that it's not the most complete coverage and that the dynamat may do a better job, but I'm happy.
It has greatly reduced the road noise. Before at 100km I had to have the radio volume on at least 30. Now I'm down to 20.