One hears foreign car going over hill (7)
I believe the answer is:
auditor
'one hears' is the definition.
(a person who hears is an auditor)
'foreign car going over hill' is the wordplay.
'foreign car' becomes 'audi' (audi is a german car brand).
'going over' says to put letters next to each other.
'hill' becomes 'tor' (tor is a kind of hill).
'audi'+'tor'='AUDITOR'
(Other definitions for auditor that I've seen before include "He checks the account books annually" , "Financial checker" , "Checker of books" , "Finance officer" , "I'll check expense involved" .)