Something is wrong with the sound recording quality on my iPhone?

I have an iPhone 4 and there's an issue with the sound recording quality.
There doesn't seem to be an issue with the microphone itself because when I call people they can hear me fine. Its just when I'm shooting a video or making a voice memo that there are problems. When I play them back the sound is really faint and there's a lot of empty noise (like the noise you get when you play a tape back in the day when there was nothing recorded on it). Maybe If I upgraded the phone it would fix the problem? I'm still running iOS 5.1.1 and don't really want to upgrade because I like to use Maps.
Thanks for your answers and have a nice day.

Added (1). There was nothing wrong with it a couple weeks ago. It just started playing up. I havn't dropped it or anything. It may have been bumped around in my bag though… Awkward: P

Could be a hardware issue

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