Bamber crept upstairs = No noise. No one woke.
It was 2am. People are usually in a deep sleep =:No noise heard.
Sheila may have been under sedation according to the 2002 appeal = No noise heard.
Her bedroom door may have been shut = No noise audible.
Bamber may have shut main bedroom door before shooting June and Neville = No audible noise for Sheila to hear.
Both bedroom doors may have been shut. Together with a gap of several metres = Impossible for Sheila to hear first ten gun shots.
A silencer was used = Minimal and reduced noise.
The twins did not wake = No noise from them.
June was shot & died in/by the bed = No noise from her.
Neville & Jeremy went downstairs = Minimal short term noise.
There was a brief but brutal fight = Noise in another part of the large WHF.
Time process from Bamber's WHF entrance to Sheila's killing ,5 - 10 minutes = Short term bits of noise. Mainly downstairs.