When I listen to music on my iphone the vocals sound weird and distorted?

I first noticed the problem when the earphones I was using at the time weren't working. Thinking it was the earphones that were the problem, I got another pair. But I've had about 4 pairs since then. The left earphone always was broken, with every different pair of earphones. When I listen to music without the earphones, it sounds fine. When I plug in the earphones they pop out off the socket very easily. And I have to physically keep the earphone socket plugged in. The problem has already happened with my old ipod too. I'm not sure if the problem is to do with the IO5 download, as I'm not sure If i have it or not. I'm now considering to stop using my phone for music, and buy a ipod classic, just incase something serious goes wrong my iphone and I can't use it. Has it happened with anybody else? Is it a problem with the phone itself or some other reason?

Take it to the apple store