I own a 5.gen iPod nano and yesterday bought a 1.gen iPhone. I get zero hiss with the nano but when I tried the iPhone for the first time I got a loud hiss no matter where I had the volume. The headphones I'm using are sennheiser CX300. Is this normal for the iPhone?

Right now I have sennheiser CX300-s and would like to upgrade. I'd like something really top end, like the Shure SE530-s but am intimidated by the over the ear cord design since I have no chance of trying them out before purchase. Are there any comparable alternatives with "regular" cable...