Get a Nissan Skyline GTR33v-spec
complete the japanese world cup and come first in all 7 races.(note:the nissan skyline GTR33v-spec is at a huge amount of horse power of
1560hp.)

How to get sound test mode
simply just complete the gran turismo champion cup.(note:you need all the licenses to open the gran turismo chapionship cup, the licenses aren't as easy as they look.)