I recently changed the heat element in the hot water tank and now when we flush the toilets or run water for very long we get a humming type sound that goes for a minute or so then seems to stop, it will also stop if we run a faucet but then starts when it is shuts off until its done.

Sounds like a classic case of water hammer (water pressure too high). However, this should have nothing to do with changing a hot water tank element considering it's happening when you flush a toilet (toilet doesn't use hot water, ofcourse). When you shut the water off to the tank to change the element, did you use a shutoff valve to the tank, or did you shut the water off to the whole house?