Insect that's loud by meadow (4)
I believe the answer is:
flea
'insect' is the definition.
(flea is a kind of insect)
'loud by meadow' is the wordplay.
'loud' becomes 'f' (A musical term).
'by' means one lot of letters go next to another.
'meadow' becomes 'lea' (I've seen this before**).
'f'+'lea'='FLEA'
'that's' is the link.
(Other definitions for flea that I've seen before include "Member of a circus?" , "Jumping bloodsucker" , "Little jumping insect" , "In one's ear, it's a stinging rebuke" , "Bug" .)