Do I need a new brake master cylinder? Buzzing noise and brake booster shaking.

My 2001 4runner is making the exact same noise as the GX in the video posted in the forum post in the below link. The booster also shakes when the noise stops and starts just like the video. The responses suggest it’s the (stupidly high priced) master cylinder. Does that seem correct? Hard to do to much additional diagnosis since my vehicle is having trouble starting so it’s parked in the garage. The brake pedal was pretty spongey before I parked it.

https://www.clublexus.com/forums/gx-1st-gen-2004-2009/954736-need-help-diagnosing-buzz-noise.html

 

Yeah. I've also seen vids where they screech like a wildcat. Seems like a 2001-2002 issue only. I'm dreading the day...

 

Got my 4runner running again and the noise disappeared so now I am confused.

 

Could be you fixed a vacuum issue? I haven't looked too deeply into the MC but often vacuum issues can affect a brake booster which is connected to the MC.

 

This probably a dumb comment/theory since I know nothing about vehicle vacuum systems, but could attempting to start the engine a few times affect the vacuum, which cause the noise I was hearing? And then the engine running again ‘recharged it’?

 

Could be. The Engine is what produces the vacuum. I don't know much about it myself.

 

My unknowledgeable brain tells me that if the engine produces a vacuum, the engine doesn’t run for a little while, and there’s a vacuum leak that that could cause the noise/issue with the booster I had. But my brain has been wrong before and it seems, based on posts I read, that vacuum leaks and booster issues lead to a firm brake pedal while mine is on the spongy side.