iPhone 4 Bottom microphone issue

Hello everyone.

Recently ive had an increased number of people coming to me with iPhone microphone issues.

Every iPhone with this issue seems to be working while recording voice and video, but not due calls(unless its with a headset)

What ive tried so far:

• 1. Replace the microphone (Dock connector)
• 2. Full restore
• 3. Software update (if possible)

Weird stuff ive read and tried:

• 4. Replace home bottom
• 5. Cut a piece of thick paper and place it on top of logic board (http://www.youtube.com/watch?v=0jhWxYTVx...)

If i take the logic board from the broken device and put it in another device with a working microphone then it still doesn't work, witch leads me to its a logic board problem.

However, something have to be causing this issue.

Normally its just the microphone that's broken, but lately its been logic board.

And i'm only talking about iPhone 4 and 4S.

Whats doing this? How to fix it?