Beat painfully (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
throb
'beat painfully' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for throb that I've seen before include "Sound of engines" , "Beat strongly" , "Pulsate strongly" , "Beat like heart" , "Pulsate with force" .)