He's always bleating about sth.

他总在嘀咕什么。

The students may be whining in their hearts, thinking that I nag too much and that I am such a spoilsport to lecture them to behave themselves before they can eat.

也许学生正在嘀咕，嫌我唠叨，嫌我扫兴，吃东西前还要听训话守则。