Nonsense! It's almost too quiet! (4)
I believe the answer is:
tosh
'nonsense' is the definition.
(tosh is a kind of nonsense)
'almost too quiet' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'too' with its final letter removed is 'to'.
'to'+'sh'='TOSH'
'it's' is the link.
(Other definitions for tosh that I've seen before include "[BLAH]" , "garbage'" , "Rubbish, nonsense" , "Pal" , "Humbug" .)