Strange rattles can be a bit frightening (7)
I believe the answer is:
startle
'a bit frightening' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'strange rattles' is the wordplay.
'strange' indicates an anagram.
'rattles' with letters rearranged gives 'STARTLE'.
'can be' is the link.
Can you help me to learn more?
(Other definitions for startle that I've seen before include "Cause to feel sudden alarm" , "Take by surprise" , "Frighten suddenly" , "Scare" , "Take (someone) aback" .)