What could be causing an electrical humming noise at night?

Hearing a persistent electrical humming or low-frequency buzzing noise at night often becomes much more noticeable because ambient background sounds drop significantly. Common causes include household electronic devices with internal power supply transformers or charging adapters plugged into wall outlets, wall dimmer switches experiencing phase-control waveform chopping, or electric meters and HVAC compressor units operating outdoors. Additionally, thermal contraction during cooler night hours can cause framing to shift slightly against electrical conduits. You can troubleshoot acoustic sources safely by listening closely or flipping breakers. You can verify that your corrective action is successful when unplugging unused phone chargers, tightening loose dimmer switches, or isolating noisy appliances eliminates the nighttime drone and restores a quiet environment.