Class D Audio amp noisy when bridged to mono

I have two Class D Audio amps set up as a three channel for HT use, and two amp modules sharing a common power supply bridged to mono for my stereo pair. The modules and power supplies are designated as the CDA 254.

In the three channel amp, only the bridged module is noisy, the module used for the surrounds is quieter. The amp for my mains, using the two bridged modules, is noisy. I am in hopes someone may have a cause for this noise, and hopefully, a cure for it. I do wonder if the noise is due to the shared chassis and power supplies? This noise, to me, sounds like a switching noise, and is seemingly double the same noise being emitted by the module in stereo mode.

I contacted Tom at Class D several weeks ago, he hasn't replied yet. Thanks for any help or ideas that you good folks can come up with.

Regards,
Dan