As you can see, when your car clutch pedal is release the throwout bearing is pulled away from the pressure plate by a clutch linkage thereby making the pressure plate to be able to press against the clutch disc that resulted for the clutch to become engaged. Also as the throwout bearing is rotating as it is being pulled away for the pressure plate.
When the throwout bearing is faulty it will produced a noise, this noise is usually howling or squealing noise that you can hear when your car clutch pedal is being release.
Another possible cause of this kind of problem is, when you release your clutch pedal the clutch is engaging and the pilot bearing that connects the crankshaft to the input transmission shaft have a stress to it. When it is faulty this will create a squealing or howling noise, you can easily determined if the pilot bearing is the problem because the noise that created is louder when you are driving uphill as opposed to a flat road.
How can you correct this problem?
Obviously with this kind of transmission problems, the only thing that you can do is to bring your car to a reputable auto repair shop and have your car examined by a mechanic; probably your car clutch or transmission assembly will get opened during the examination of the mechanic.