There were commands included to change the gain.
If you don’t know what gain is … i suppose you can read this: Thoughts on optimizing gain
But it doesn’t completely apply to 978 … 978 you want it quite a bit quieter than 1090, different demodulation scheme.
No that’s not it the range is just atrocious.
Probably interference or just noise as in a noisy HDMI cable near by.