Buzzing sound at start up

[3gsdad]

Hello all,
I have been a Toyota owner for 15 years and just bought my first 4th gen 4runner. When I start up the truck there is a loud buzzing noise that last for several seconds. Sounds like ABS powering up or something but it is super loud compared to all my other Toyotas. Did a search but did not find much.

What is it? Should it I be concerned? and can I make it go away or be quieter?

 

[nevada]

id guess the master cylinder building pressure for the power assist.

next time pop the hood, and have someone start it so you can listen. and even rest your hand on the mc, you should be able to feel the pump running.

 

[DC runner]

Seconded. The way you describe it, brake mc building pressure. Mine always does it, right at start up for just sla bit.

 

[seneam99]

I have the same issue with my 2008 4Runner. Braking seems to be fine. Never heard it before last week. Listened under the hood and it is definitely coming from the mc. Does it need to be replaced?

 

[SocalSam]

I have the same issue with my 2008 4Runner. Braking seems to be fine. Never heard it before last week. Listened under the hood and it is definitely coming from the mc. Does it need to be replaced?

Mine started to screech loudly which turned out to be bad pump motor. Braking action was not affected. I replaced pump/accumulator assembly from a 2003 Lexus GS300 for $60 and 2 hours of my time. Yes, I am economical.

 

[4R005]

[MENTION=94128]3gsdad[/MENTION]
If you have air suspension at rear axle, it can be the air pump charging up the the air bags to normal height setting ( rear axle ) when first start of the day with your truck. Noise from air pump which is mounted just aft of vehicle rear axle on frame on driverside would be much louder than ABS pump ( on my '05 T4R w/V8 ).