There are a few reasons why your alternator might keep going bad such as rusty latches under the car. You may also have leaks, dents, or parts that need to be replaced on the vehicle that are effecting your alternator.
If your battery is not up to par could cause this and of course a short in the system too.
When your battery does not get charge.
If bearings go bad they will "squeal"
If the car won't start, jump it off. While it is running, remove the positive cable from the battery. If the car dies, then your alternator is bad. If it keeps running then you may have a bad battery.
Normally this is the bearings going bad.
The battery will run down and he engine will stop. You will not be able to start the engine. The alternator keeps the battery fully charged.
There are several signs that an alternator is going bad. A few signs are dim lights, smell, warning lights, and a dead battery.
Have the charging system checked. Possibly loose or corroded wiring, a loose alternator belt, or a bad alternator.
good
Alternator is going out? battery is going bad?
A bad alternator will make whats called a whirring noise. It could also make a low growl. This is just the bearings going bad. If your alternator is not supplying any power, it has nothing to do with noise typically.
The diode in the alternator is probley going bad, Check charging system. And replace alternator.