The noise is simply caused by the Gasoline-engine.

In a stealth scenario they could use batteries (as full or part-time energy source)

Impressive is the ability of the robodog to keep upright
in a very unstable position.
Not like these japanese human-bots who are build to
have low instability. (big feet and such)

The bobodog itself is not really useful yet (a dirtbike
or quad is a better choice)
But the technology itself is impressive at that stage.

--

The second bot is impressive for using such a very
simple solution, and actually revinventing the wheel.

This would make it a much better system for outer planetary
rovers, that the classic rigid wheels.

When making these "flaps" to change between an open and
closed (wheel) form, you could
even seamlessly change between a driving and
walking behaviour.