Is it normal to hear hum when playing records?

No, a good vinyl playback system, correctly set up, will be quiet, with no noticeable hum.

Hum really just indicates a problem. It can be mechanical or electrical in nature but either way, where hum appears, it needs to be tracked down to the source and resolved.

Bad earths/grounds are a common cause of hum. Ground loops are a variant of this and can result from bad cables, incorrectly earthed equipment, power cables and mains outlets. Cheap phono preamps, cartridges and cables will always be noisy. General equipment set-up, installation and arrangement all can contribute to this.

Mechanical hum can originate from a turntable motor or mains transformer. Motor hums can often be resolved with the right attention and some new parts. Mechanical vibration from other equipment can also be coupled through a turntable, back into speakers, creating what’s called a positive feedback loop.

Positive feedback loops can very quickly go out of control and destroy speakers and even amplifiers, so if you have a hum that appears to be coupled through your turntable, seek expert help immediately!