This song would've played whenever the player wins a boss battle at certain tournaments that had them. However, in the final game, winning a boss plays the same song as for winning in battles. Judging by the filename, it's possible that this theme was intended to be used when beating the bosses in the early Mission Mode as well.
STRM_N_TRUCK_N.brstm
The second section/piece of Wario's Gold Mine (meant for when inside the mine) originally had an opening to its track. Although it is technically not unused, this opening is never heard since the race always starts outside. In addition, no online tournaments taking place in this level start inside.
Sound Effect[]
An early trick sound effect. Compared to the final version's, it has a higher pitch and it is also slightly longer. A similar sound (if not the same) can be heard in a prerelease trailer. Curiously, a variant of this sound was used in a few competitions/tournaments, more specifically the ones that had the player race a Wiggler, when the said character does a trick (SE_CC_HANACHAN_JUMP_ACTION). However, other than sounding slightly different than the unused variation, it is also sequenced with both the early and the final trick sounds being streamed. This sound would later be used in Mario Kart 7 when the player does a trick in both the Rainbow Road tracks.