Probably isn't the right part of the forum to ask this. (unless you are working on a plugin or something?)
Anyway..
I guess the "screeching" you are referring to is the background noise before you noise gate kicks in.
My best guess is that you are using a noise reduction filter and a noise gate and have a fairly noisy ambient where you are recording..
If that is the case, you have two options.
- Use more noise reduction (though you might loose dynamics in your recordings)
- Try changing your attack/release on your noise gate so it closes quicker.
Those two will help somewhat if the problem is what i think it is.
If that isn't the case.. i don't know.
I would try changing your mic input from 16bit to 24bit, or even 32bit (44khz or higher) and see if that helps.