I have ensured that the access to the microphone is allowed or turned on in the privacy settings. The mic works fine on other apps, i.e. FaceTime. So that rules out hardware failure. I have also tried reinstalling the app. Any other suggestions?
Try to reboot the iPad (hold the sleep button until the red slider appears, slide the red slider and once the screen is blank press the sleep button again). This has worked for me.
this is was quite common problem with iPad 2 and in my case, trying to suck the dirt out with a vacuum cleaner worked!