Volatile rodent found in Morecambe, perhaps (7)
I believe the answer is:
erratic
'volatile' is the definition.
(thesaurus)
'rodent found in morecambe perhaps' is the wordplay.
'rodent' becomes 'rat' (rat is a kind of rodent).
'found in' indicates putting letters inside.
'morecambe perhaps' becomes 'eric' (Eric Morecambe).
'rat' going inside 'eric' is 'ERRATIC'.
(Other definitions for erratic that I've seen before include "Unstable" , "Random, unreliable" , "Wayward" , "Behaving irregularly" , "Not regular in pattern" .)