Timothy Down said he was so worried about noises coming from Natasha Bradbury's Haverfordwest flat that he hung his mobile phone out of the window.
But he told Swansea Crown Court he was advised not to get involved.
Miss Bradbury's ex-boyfriend Luke Jones, 33, denies her murder.
The 27-year-old died from blunt force injuries on 22 February, which Mr Jones said she caused to herself by falling down.
Mr Down, who lived in flat D, said he was woken by the sound of "serious, heavy banging" coming from flat A.
Paul Lewis, prosecuting, asked Mr Down why he did not call the police and he said he rang his father who advised him not to get involved.
The jury heard that on the night she died, Miss Bradbury had been exchanging texts with a man she had met at a friend's house, but the messages stopped suddenly at 22.10 BST.
The prosecution claim Mr Jones killed Miss Bradbury a short while later, because at 02:48 BST he called for an ambulance and told the operator she was already "freezing cold" and that "her lips are blue".
After his arrest Mr Jones, from Milford Haven, gave prepared statements to the police. They said Miss Bradbury had caused the injuries to herself by falling down.
The case continues.
A neighbour tried to record the sounds of a woman being beaten to death in Pembrokeshire, a jury heard.