When does it freeze after the strap loader? Also, when you say "character packs" I'm assuming you must mean with custom menus or something? If so, what files came in the character packs? While I might not know exactly which file does the specific frame of what you mean, I can recognize what would NOT have anything to do with it so that you can test the other files.
By that I meant I downloaded a bunch of characters from here.
It freezes before the "Online interactions not rated by ESRB" message can fully fade in..
I know it's not the console cause I tried to test on both my wiis.