Brakes and more...

So I haven't posted anything in while, but 3 weeks from graduation and things are getting hectic!
1)Anyway, I recently had issues with brake fluid leaking somewhere. When I finally had time I took it in and was told it was the master cylinder. The part came in and the installed the new master cylinder. Things seemed to go well, until, I started noticing that sometimes the pedal would depress completely and the car would barely stop. I took it back, they bled the brakes and said everything was fine, there was some air in there...then 2 weeks later, i'm driving had slowed down to make a turn and the car DID NOT STOP...brake pedal to the floor. I used the emergency brake and it thankfully helped stop the car . I then had the same shop tow it on Monday and they said the brand new master cylinder that they had installed was defective and said they replaced it, this was yesterday. Today, i noticed that the brake fluid light coming on and off, as if the fluid was low. WTH is going on!?!?
2)I've also noticed a strange pop sound when turning in motion, i.e. around a corner. It doesn't do it the whole entire time, just as i turn. They said they did a rebalance on my car and would think they would have noticed something with the control arm or bearing.
3)This one has been a problem since i got the car. When going up hills there is a strange vibration/sound (kinda like a long fart), that seems to start from the front and moves to the back.
Any suggestions on either of these would help.