Its natural for hamsters to do that. They probably want something... If you want them to stop you can get some chew treats or any kind of dog biscuit works too.

Syrian's (teddybear hamster) usually live about three years.The smaller varieties, like the Siberian and Campbell's, not quite as long, usually around two years. The Roborovski is the dwarf hamster exception, and has been raised to three years in captivity.