There is a knocking sound and grinding sound coming from underneath my car. I know the grinding is my breaks. But When i hit the brakes it starts to knock and feel like a loose banging. I also have a sound coming from the front i think, could be back, underneath that is a loud obnoxious sound that sounds kind of knocky/screechy. I'm not sure what it is. My brother suggested ball bearings. Is he right? The noise is worst at a slow speed and right before i come to a complete stop.

Hit in the rear axle may have damaged bearings or brake parts. Jack up the side you hear noise from, put on stand, then have helper rotate wheel while you look underneath and listen to see where noise is coming from. Use length of old fuel or heater hose, one end in ear, to locate exactly where noise comes from.

Sounds like the brakes - take it to a repair shop.

I would pull the wheels and look for something loose on the brakes, such as a spring or self adjuster. Also look at the backing plate to see if it is tight.
Keep in mind it may be something covered by the car's warranty.

It sounds like the brake pads are metal to metal, when you turn the flexing of the wheel makes them touch the rotor and grind. This can rarely be caused by a badly worn wheel bearing as well, have both brakes and wheel bearing inspected.

The sound could be a warning that the front wheel bearings are worn out...this should be a free inspection at your local brake/suspension/muffler repair shop...the bearing seals can deteriorate, and allow foreign objects (small dirt) to be exposed to the bearing...Please have this checked...the grinding probably increases with speed...the faster you drive...Hope this helps.

could be loose wheel nuts
take the car to a specialist brake shop for a pad/rotor /drum inspection

First thing with brakes is to check the lining thickness. You can usually see the fronts through the wheel, or look underneath. If you have drum brakes in the back there may be a rubber inspection plug.

But if linings are ok, another risk is wheel bearings. You would then feel it as a vibration in pedal, and through steering wheel if a front bearing.

With the light, have the ABS code read with a ODBCII module. Autozone can do this for free.

are your motor mounts good?

Squealing usually indicates that the brakes are in need of replacement. There is a small piece of metal that as the brake pads wear comes in contact with the metal rotor. When the pads get close to being worn away the tab touches the rotor and it squeals. The tab can also click.
When the pads are worn away completely the metal backing comes in contact with the rotor and it grinds. Grinding is bad. It means the car's brakes are metal to metal. This will cause damage to the rotors resulting in an even more costly brake job.
You should have it taken care of ASAP.
I hope this helps.

Ok, it could be a few things, 1. bad break caliper. 2. if you have ceramic breaks, it could be a cracked brake pad, and if they are not ceramic they can still be cracked. 3. if you drive a lot then it could be that you need new breaks again.. 4. also have your back breaks checked along with the front ones..