[Richard]

The 1/2 bath discharges directly into the waste tank. The rear bath has to discharge into piping that travels to the waste tank. The purpose of the pressurized hopper is to force the waste through the pipe to the waste tank.

Is the hopper on the rear bath emptying?
What happened what you lengthened the cycle?

I watched the video with the sound turned up. The hopper is pressurizing before the flap closes to seal the hopper. That is what you are hearing. If air pressure and water pressure are correct according to the manual, and lengthening the cycle doesn’t correct this, then your next move is to remove the sequencing valve, disassemble and lube with light silicone grease. There are links to the manual in the documentation section, and Bare @"rheavn" has posted a thread on adjusting the toilet.