Hi @Radnor, welcome to the Sonos Community!
If your TV sound is jumping/intermittently glitching but music streaming works fine, then it’s likely a connection between the TV and Sonos Beam.
To rule out the basics, I’d recommend rebooting the TV and Beam by powering them off for a few minutes then back on. While they’re powered off, try re-seating the HDMI cable between the TV and Beam.
If you’re still having sound issues with TV audio, try another HDMI cable or the Optical Adaptor that came with the Beam and see if this resolves your issue.
I hope this information helps!