2007 brake noise issue...
 

I have a 2007 4runner that has recently starting making an intermitant squeal noise near the brake pedal next to the firewall. The squeal noise lasts for about a second and happens every 10 seconds or so and a light vibration is felt on the brake pedal. The sound happens randomly, on or off the brake, in motion or stopped. There is also a slight drop in rpm's and a sound/feeling happens like when the A/C is turned on. I checked under the hood and there is a yellow canister to the top and side of the master cylinder unit. When this unit engages is when the rpm's drop and it shakes a little, I believe this is where the squeal is coming from as well. What is this yellow canister? Any thoughts one what this issue can be and how to go about servicing it/costs.
I thought is might be the brake booster assembly or ABS actuator motor. The brake operation of the truck is not effected however, so far it stops normally and the brake pedal pressure is normal as well.