Why is my Iphone's facetime volume so quiet now?

Hey!

I have a North American (Canadian) iPhone 4 running IOS 4.3.2. Prior to this I had never updated the OS from 4.1.1. I have never jailbroken/unlocked my phone or attempted to hack it in anyway. It has always been in a case and has never experienced any form of physical damage.

Anyways, I am in Australia now, and beginning about a month ago, the volume on facetime calls just randomly dropped to the point where I can hardly hear anyone unless I use headphones, and even then I need to have the volume at maximum. As soon as I begin a call, the volume on the phone completely drops. The sound of the ringer is quiet, and the other person's voice is quiet. However, anyone I call can hear me just fine. This problem began and has continued prior to and after updating the ios.

I've tried using the volume buttons, adjusting the volume in settings, closing all other apps, resetting the iphone, backing up and restoring the iphone, and none of this has worked for me. I don't have anything covering the speaker or microphone, and I'm not covering the speaker with my hand or fingers. It doesn't seem to be a problem with the speaker, because I can play music from the ipod or games without the headphones and they play at normal volume. It's just facetime that causes a huge volume drop. And I've tried this with my entire family back in Canada, all of whom have their own iPhone 4's (there are 4 of them), and it's the same in all cases. They can hear me totally fine, but I can hardly hear them.

I've looked at these similar posts and it seems like nobody has really found a solution in those cases either:

https://discussions.apple.com/thread/2616873

https://discussions.apple.com/thread/2476169?answerId=13298016022#13298016022

https://discussions.apple.com/thread/2598680?messageID=12356594

Is there anything else to try besides bringing it to the Apple store? I just don't get it. It only started about a month ago, it was never a problem back home in Canada, and I haven't done anything to my phone that would bring this about.

Any help would be greatly appreciated!

In the event that it is a problem with my phone, does my warranty extend from Canada to Australia? I bought my phone on September 9th, 2010, so it's within the 1 year warranty period.

Thanks for your help!