rajul,
IMHO, the sound level on the video doesn't accurately capture the sound of the ST 90 w/MCP. The video has a loud drumming sound that's hardly noticable in real life.
The other plane you're hearing (and sometimes seeing) is my nephew's UCD, which is powered by a TT Pro 61. His UCD is fairly quiet, but the camera makes it sound like he's got a DA-150 in there.