To unlock secret music, go to Tota K.K. and say yes when he asks you to do something. Then type "Two Days Ago" or "I Love You".
To get 30,000 bells, go to Tom Nook and enter:
WB2&pARAcnOwnU
jMCK%hTk8JHyrT
You can use it only 3 times a day and have only 90,000 bells in your wallet.