I'm running a magnum 350 canister filter on a 55gal planted freshwater community tank. I bought it used, along with the tank, 2 years ago. It's running fine, but the impeller is making a significant rattling noise as it runs. It sounds as if the magnet is off balance or something. Has anyone else had this problem? I know that both the magnet and the impeller/shaft are available as replacement parts, but I was hoping to get an idea as to weather it would be of any use to replace either part before I spent the money on it.