Merit increase having eliminated new impediment to hearing (6)
I believe the answer is:
earwax
'impediment to hearing' is the definition.
'merit increase having eliminated new' is the wordplay.
'merit' becomes 'earn' (I've seen this before).
'increase' becomes 'wax' (waxing is a kind of increasing).
'having eliminated' indicates named letters should be taken away.
'new' becomes 'n'.
'earn'+'wax'='earnwax'
'earnwax' with 'n' taken out is 'EARWAX'.
(Other definitions for earwax that I've seen before include "Shell-like secretion" , "Waxy secretion impairing hearing" , "Secretion that can impair hearing" , "Otic deposit" , "Potentially deafening build-up" .)