Good afternoon~friends,thanks for taking time to read my topic. Could anyone help me out?

This is the circuit of my audio.I would like to know why the output was wave if the amplifier didn't connect U27?  What lead to this problems? I have tried any ways I can thought to track troubles. Firstly, I reviewed the switch,it's normal. Then, .it occurred me that maybe C33 is the root problems (this is the C33's datasheet:http://www.kynix.com/uploadfiles/pdf8827/C330C104K2R5TA.pdf) but it doesn't have any advantage after I demolished it.Well, I still feel it's C33 that lead to these troubles.Could Anyone help me to have a look and solve it?

Thank you in advance!