A:Answer The U7 (like most modern TVs) uses a 2-prong power cable. A grounding hum can be due to multiple issues, and not always the lack of a plug with the extra grounding prong. The hum can be due to interference caused by an A/V cable (even HDMI), mismatched power requirements, a failing transformer, etc.
From experience, audio equipment is much more susceptible to a grounding hum than TVs with built in speakers - regardless of the electrical plug.