The outside unit buzzes and will not turn on

Not really just let unit run and watch what causing the rattling sound.
Maybe unit is not level or even fan blade bent

there is a dual cap in unit. kill the power and remove the silver cylinder. on top it has 3 places it can put wires. F, H, C. write the colors of wires and where they belong. take part up to granger and buy. 30 bucks most. replace. if same problem do the same with fan motor, around 60.

Is the compressor running? Check the circuit breaker or disconnect that is close to the outside unit if it isn't. It may be tripped on high pressure since the fan isn't running. If the unit has power, use a screw driver or something that will reach the fan blades and spin the fan to make sure it turns freely. If it doesn't the fan is probably bad. Next, check the capacitor for the fan motor. If it looks swollen then it is bad, otherwise check it with a multimeter. Most heating and air suppliers will test it for you. If the capacitor is good, the problem may be you fan motor.
You can check the fan windings with an ohmmeter.

honestly, unplug the garberator, tap it a few times with yourwrench, not too hard.. and try again.. if it does not free up, the motor itself is finnished.

YOUR OUT SIDE CONDENSOR FAN MOTOR HAS WENT BAD ,REMOVE THE OUTSIDE FAN AND MOTOR TAKE WITH YOU FOR A REPLACEMENT MOTOR MAKE SURE THEY MATCHDON'T KNOW WHERE YOU LIVE BUT R.E.MICHAEL CO. IS A GOOD COMPANY

The motor gets hot from over amping for various reasons. Nine times out of ten the fan motor needs to be replaced. This really isn;t something that most people can do without proper training. The way it's done on the outside chance that you have the mechanical expertise is, you shut the electric off to the A\C, with a 5/16s driver unscrew the sheetmetal screws at the top of the unit and gently lift the lid and unbolt the four bolts holding the motor turn over lid, pull the electric leads of, making notation where each goes, back the retainer screw off fan blade and remove blade. Unscrew belly band pull out motor. Take this motor to the parts supplier to match exactly the right motor. (All of this is probably academic because almost all supply houses do not sell to the public, it's too dangerous) If you get the motor just reverse everything you did to take the other one out. The best route is to spend a couple hundred dollars and pay a Tech to do it right, It's more involved than an electric or plumbing fix. One other thing to get you by. Get a square box fan and fix it to the top, expelling the air upwards, turn on high and turn on unit, This usually works til a Tech arrives. It may not be as good as normal but it will cool to some degree. Good Luck

Check the start capacitor. You may be able to see visual deformaty, otherwise, use a meter. The buzzing is most likely the contactors closing which uses a seperate 24v supply..

When ever you hear a buzzing like you are hearing means one thing one of the fuses on the outside disconnect box is bad. Only getting 1/2 the power. Find the bad fuse and get the same size and will be good to go. ken

Even when the power is off at the unit outside the thermostat will supply power to the contactor of the outside unit. This may give a hum or buzz as you stated. If when the power is on to the outside unit the fan tries to start but only hums the motor may be bad. Does the compressor start and run?

the spring is stuck in the release pin. usually wrapping it in a hot steamy towel for a while works. but what you might try is also wrapping it in a hot steamy towel for a frew min about 15-20 then taking a screw driver and lightly tap around the outside edge with the handle. do not hit hard like a hammer just light taps all the way around and that may help loosen the spring.