electric brake booster non vacuum

OK 2014 TRD off road. Why does this thing click and make weird noises a few seconds when when cranked and sometimes after running a while when brakes used?

 

It isn't niticable to my passengers but I can feel it when it happens.

 

The system is different due to ATRAC. it's normal

 

I read all the atrac jokes. Is this a serious comment or joke?

 

Joke? No, the ATRAC system uses a pump and accumulator for brake pressure. There is no vacuum assist. You'll notice that the pedal feel is the same with the engine off for a bit longer than a vacuum setup, there is more residual pressure in the accumulator than there would be vacuum.

It's probably not all that different than GM hydroboost, but I'm speculating a bit on that.

 

OK thanks.