As Bruce suggested, I wonder if it's something to do with an audio return channel from the TV.
Have you tried a different HDMI input on the TV?
You could also try setting up a new input (digital from another source e.g. your G98 aux output)) using the 'wizard' to see if that makes any difference.
Main: G65, MD600, MS600, 598DP, HD621, DSP5200SE, DSP5200HCSE, M6 & D1500.
System 2: G91A, MS200, DSP5000 (96/24v1), DSP3300.