下课铃是好声音
[xià kè líng shì hăo shēng yīn]
'Xia Ke Ling Shi Hao Sheng Yin', it's an ironic way of saying the 'ring tone at the end of class is good voice'. For students waiting for the class to end, the bell seems to be music to their ears. This phrase shows that they are tired from studying and are looking forward to relaxation or recess.