1. Depending on your water pressure, a 'hissing' noise of rushing water may sound from the faucets. If the water supply pressure is high, check the noise while closing the faucets gradually. 2. A ‘humming’ sound around the washer’s water supply valves during water supply is a normal sound which occurs as the valves operate. And a ‘knocking’ sound during water supply may occur when the valves close. 3. If the inlet filter is clogged, a ‘hissing’ noise may occur because water is forced through a narrow space. If the inlet filter is clogged, clean it.