I hear a buzz or static on the line, is this normal?
It is not normal to hear buzzing. This can be caused by interference with cordless handsets or faulty grounding in the phone circuitry. Try another corded phone to see if the buzz stops.
I hear a constant hum on my IP phone. What could cause this?
There is a good chance that hum is being caused by an incorrect power supply (if you are not using POE (Power over Ethernet)). Check with the manufacturer for the correct power supply and check that grounding is correct.