How would I know if the length of the cable was an issue?
Yep, you are listening for sound degradation. Easiest way to find out what this sounds like is to switch in longer HDMI cables until the degradation is obvious.
When HDMI cables are used as intended for HDMI, it is easy to see the effects of overlong or poor quality cables on video. Blockiness on the screen, dropped frames, noise. HDMI is designed for an error rate of about 1 in a billion bits which I think translates to about 70 CDs per error!

