Grinding Noise while Gas/Brake [Car On Park]

Hi All,
I really need help after going to Toyota Dealer & local mechanic.
I hear a grinding Noise during different situations
-Car is moving and I push the brake, at the end of the Push I hear the sound [if i push just a little bit i don't hear the sound, it has to be a heavy Push to slow down faster, but not like an immediate full stop to avoid an accident push][intermittent]
-Turning the car on, when the gas engine kicks in. [now it turned into Always]
-Car on park, Air Condition is on, Sound can be heard when the battery get low and gas engine kicks on.
-Put the car on reverse,on releasing the brake, I hear the sound. [intermittent]


I was able to record the sound
Car on Park,Car is in Ready [turned on, EV light on, gas engine not started], When I push on the gas to kick the engine to start, you can hear the sound on second 4,11,18. [Sound is Always]



The Dealer did a full CHECK, said I need to replace brake fluid and brake adjustment
Local Mechanic checked my brakes and fluid, said its fine, he just adjusted my brake on the back and he claimed that the noise will go away after 2 days of driving, which doesn't make sense to me at all since the noise is really increasing over the course of the last month

the noise is coming from near my feat that's where i placed the phone to record it, I feel like some gears are grinding. my personal opinion is that it has something do it with starting the gas engine and has nothing to do with the brakes

car 2016 Prius C persona Series, 45K Miles, last oil change on 43K.

 

-after driving for around 10 min, made a full stop, put the car on park, released my feet from brakes, heard the noise
if the car is moving, I never hear the sound if i am accelerating wither its in ECO zone or power zone. i only hear it with a heavy push to the brake [example : a push that can take my car from 40 to 20 mph in 2 seconds]

 

Hi Bisco,
I bought it on 42.5K mile 2 month ago, and on the first week I heard it like 2 times i didn't bother with it, but now it increased, Do you know what could it possibly be?
the mechanic checked my rotors/drums, he said they are good, I can go to another mechanic to get them re-checked.
the reason am saying i don't think its the brakes because I can hear the sound when the car on Park,EV and I press Gas to start the gas engine, i hear that grinding. am not an expert, but doesn't that rule out the brakes?