Acer 5920G continuous siren sound

I've been using a couple of very simple desktop recording programs, and either the programs or me must have annoyed the microphone. It started setting itself to the maximum = +30dB (or more like +300dB) boost, which resulted in the awfully loud continuous high pitch tone (audio feedback?) about 10-15 seconds after every time Windows (7) started up. I learned how to quickly bring back the boost to 0 before the laptop went crazy, but wasn't smart enough to just disable the damn thing. Then it just started getting worse and now the unbearable high pitch tone starts half-way thru start-up, and the laptop (Windows Explorer?) hangs completely, sometimes only letting me move the cursor for a couple of seconds on a black screen. The only option I see is somehow learning how to disable/disconnect the mic from Command Prompt. That's the very last thing that works correctly. Anybody?

 

The modem board (located below the wireless card) is likely unplugged.

 

Thanks for your quick reply!
So what you're saying is hardware not software, i.e. a trip to a shop? (I don't quite dare open up a laptop.)

 

The microphone might be set to always on, or switched to 'listen mode' in windows settings. This will cause a loud feedback loop.

Go into control panel, sound, find microphone option, click properties and make sure that 'listen mode' or something similar is not ticked.

I'd give this a try before taking it to a repair shop