To guffaw in higher notes is extremely funny (10)
I believe the answer is:
uproarious
'extremely funny' is the definition.
(I've seen this before)
'to guffaw in higher notes' is the wordplay.
I cannot quite see how this works, but
'guffaw' could be 'roar' (I've seen this in another clue) and 'roar' is found within the answer.
'higher' could be 'up' and 'up' is located in the answer.
'notes' could be 'ious' (I Owe You notes) and 'ious' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for uproarious that I've seen before include "extremely funny" , "Side-splitting" , "Very noisy (and funny?)" , "hysterical!" .)