Malfoy cast Muffliato charms on her frequently, and after the first day, Hermione managed to ignore the horrendous buzzing noise and use the time to work on her Occlumency. He used it every time they were at the Ministry, when he had conversations with his mother, when he used the bathroom, and she had to linger outside. The fact he knew the charm tickled at her brain. It wasn’t a well-known spell, but he obviously favoured it. She also attempted to lip-read but gave it up. Both; it made Malfoy put her in a corner facing the wall, and she was terrible at it. 