Let rip, yelled and began moaning insufferably in a grumpy manner (3-10)

'grumpy manner' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'let rip yelled and began moaning insufferably in a' is the wordplay.
I cannot really see how this works, but
an anagram of 'let' is 'lte' which is within the answer.
'a' could be 'per' (eg 'one a day' means 'one per day') and 'per' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?