Bed crawling with lice making a level of noise (7)
I believe the answer is:
decibel
'a level of noise' is the definition.
(I've seen this before)
'bed crawling with lice' is the wordplay.
'crawling with' indicates an anagram (letters crawl around).
'bed' mixed up with 'lice' gives 'DECIBEL'.
'making' is the link.
(Other definitions for decibel that I've seen before include "Unit of measurement for loudness" , "Noise unit" , "I relate to volume" , "Measure of sound" , "Measure of noise intensity" .)