Real easy, take my words on what I say.
1... The noise you are hearing on start up is your serpentine belt (as what was said) or the single belt (because I am not sure of your setup). Why the noise? The noise is being made because your alternator is on high load trying to recharge your battery after start up. The noise goes away after awhile because the alternator has done its job to charge the battery so now it is relaxed ("max" load is gone). Fix, possible a new belt, but more then likely you need a new belt tensioner and it goes without saying to replace the belt as well.
could look something like below (again not sure of your model).
Now if your car as a single belt to the alternator, then it can be a simple belt tightening that is all that is needed to stop this noise.
2... Brakes. Yes there is (or I should say "more then likely", but most do have them) a warning tab (as what Hellraiser was saying) on the brake pad to warn you that your brakes are low. When this warning tab is hitting the rotor "all the time" it will make a noise when the brakes are on or off.
Fix, replace your brakes as soon as possible.
EDIT... I wanted to show some photos of the brake pads, but needed to get the little one off to school.
This 1st pic shows the low brake warning tab and the 2nd shows a brake that is worn down to nothing (also would mean new rotors are more then likely needed because resurfacing them is unlikely after going this low).