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I've had my RAV4 Prime XSE for a few weeks now and loving it, but I've been hearing what I can best describe as an air "hissing" sound when I press the brake pedal. I think it might kick in when the mechanical braking takes over? I tend not to hear the sound right away while the brakes are doing regen when I first depress the pedal or if I'm only braking lightly, but I need to pay closer attention.

Just wondering if this is normal or not, and do others have the same observation? I tried to do some google searching and there were mentions of things like a "brake booster" and something about a vacuum, and that the sound is air leaking out which is a bad thing, and other results saying it might be normal to have that sound because of how the "brake booster" works.

Thanks in advance.
 

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2021 RAV4 Prime XSE (+weather +audio) Silver Sky Metallic
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I’ve assumed that sound is the mechanical (hydraulic) brakes taking over as you noted. There is also a slight difference in pedal feel when this happens so this makes sense. I’ve also only noticed the hissing sound if I’m braking slowly below 5mph or so.
 

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2021 Rav4 Prime SE X2
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I've had my RAV4 Prime XSE for a few weeks now and loving it, but I've been hearing what I can best describe as an air "hissing" sound when I press the brake pedal. I think it might kick in when the mechanical braking takes over? I tend not to hear the sound right away while the brakes are doing regen when I first depress the pedal or if I'm only braking lightly, but I need to pay closer attention.

Just wondering if this is normal or not, and do others have the same observation? I tried to do some google searching and there were mentions of things like a "brake booster" and something about a vacuum, and that the sound is air leaking out which is a bad thing, and other results saying it might be normal to have that sound because of how the "brake booster" works.

Thanks in advance.
There are several burps, farts and other noises you will hear when the car is on and even off sometimes. All normal.
 

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2021 RAV4 Limited FWD
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Mine does the same thing, and it is not a hybrid. I attribute the noise to the brake pads rubbing against the rotors. Perfectly normal.
 
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