Inserting 3. 5 inch floppy-disk into a floppy disk drive, with the typical sliding sound first and then the spring-activated locking mechanism snapping it shut.
Inserting a large 8-inch floppy-disk into a shugart floppy disk drive and closing the plastic front bezel drive latch. Noisy recording with the fan of the enclosure and neighboring system humming along.
Inserting a 5. 25-inch floppy disk into a micropolis 1053 i metafloppy floppy-disk drive. That's the sliding sound at the beginning. The second knock-knock type of sound is the press-down-and-hook drive latch being closed. The micropolis 1053 is a two-drives unit for s-100 bus early computers. This sound was recorded on the upper floppy-drive.
