Clicking on lower right screen on iPhone 5c?

I've had my iPhone 5c for about a month. I have loved it up until now she I have noticed that if I lunch my fingers up and down on the lower left corner there's a clicking sound, sometimes louder than others. This is really annoying and the worst part is...I bought my iphone from an apple shop in Hong Kong, to save money. Which means the warranty is only valid there. I need help. Any ideas on how much this might cost to fix? I live in New Zealand by the way. I'm really annoyed as my iphone has been great until now and I can't afford to make the clicking any worse or therefor breaking the phone.