I too had strange results when I first tried the uBitx, very similar, though not exact. Would check that the SWR/Power meter is rated for the frequencies being measured. the first one that I bought dropped off at lower frequencies. Checked closely and it was a CB (11m) rated SWR meter.
As to the buzzing, I found that the volume control at minimum created the buzz on transmit (I had turned down the volume because the normal side tone is extremely loud). The other possibility is that the power supply is causing the buzz if it is close to max rated current.
Since it is connected to a dummy load, the other thing that I ran into that had similar symptoms is when connected to an off center fed dipole (OCFD). The RF on the braid was getting back into the audio on the ubitx and causing buzz on CW, distorted audio on SSB. Fixed with RF ferrites clamped on the coax and improved ground in the shack.
The above are my experiences, and may not relate to yours.