Vostro 5320 - Microphone issues

Hello, 

I'm just wondering if there are any known issues with this model and the microphone? We have around 19 of these laptops and it now looks like the microphone on the third one has stopped working. I've gone as far as doing a fresh Windows install and the issue remains. There doesn't seem to be much info on the model when searching so I'm wondering if anyone here has experienced issues with the microphone on theirs?

When you try to do a mic test using the built in sound recorder, the input on the wave graph just shoots up to the max and stays there, then when playing back there is nothing. Usually the sound will go up or down depending on what is detected. I've ran driver updates, bios updates and Windows updates, but none of this has helped. I also uninstalled all sound devices from the device manager, then rebooting the system so it installs the basic drivers, but this also doesn't help. The fact I've done a clean install of Windows should eliminate any driver issue.

To me, this seem like a hardware issue. From having a quick look, it appears that the camera and mic are part of the same board. Can this be easily replaced, or is it soldered in place?