Advice please.

[Asgardian]

Okay so I have a Canon 550D which I use for making short films, extremely amateur ones at the moment, and I bought a Sony shotgun mic by recommendation from a guy who seemingly knows what he's on about, saying that it was the best value, low budget etc etc mic available, anyway it was ok except for there being a horrible amount of hiss which basically ruined a few hours work. So we decided to buy a new mic and after watching many video's on youtube of tests of certain mic we had to choose between the Rode VideoMic and the Audio Technika ATR-55 (6550) , we went for the ATR-55 based on the higher volume of very nice sounding test videos of it on youtube, so it turns up, we plug it in and low and behold have the exact same problem, now this is no doubt something we're doing wrong as I don't believe two different Mic's would have the same problem from new.

Help please, what are we doing wrong? Why does my audio sound so bad? Don't get me wrong, you can hear everything else clearly and it sounds great but there is a constant hiss and it is pretty loud too, also we tried recording on to a Sony dictaphone too, which ridiculously records better quality audio than plugging these Mic's into it does!

Thanks in advance for anyone who can help,

J