Almost any turntable will pass a knocking on, suspended ones less so. Don't worry about it.
The vinyl-covered particle board is actually very good at damping vibrations, much better than a plastic shell.
The SL-23 I had was bought with the intent of converting it to a record cleaning machine. When I put on a headshell with cartridge to try it, I was startled at how good it sounded. It was given to the daughter of a friend, who was interested in older music and records.
Put a Blue on, align it properly, and enjoy.