Loud humming noise when using the hot taps on any tap in the house also when using the flush on the toilet. Also when using the bathroom sink the kitchen starts smelling like sewage. Please help!

Can you localize the hum? You have this hum on both hot and cold? If you have a PRV installed? Install? Describe the hum. Back to you, Tom

Its only on the hot tap. It sounds louder upstairs. What is a prv? Many thanks

A PRV is a pressure reducing valve located at the place the water and if your home. You mentioned the toilet, does it make a noise also? You get a hound from every how water tap? Can you furnish more details? Back to you Tom

Where would the prv be located to in the house? It makes a noise if any taps are on or if washing machine is on, sometimes it just does it with no taps or washing machine on. Every hot tap we use it makes a noise when we turn the tap on faster. We rent the house of a landlord, the house was built in 1930s I think.
Many thanks

A PRV is a pressure reducing valve located at the place the water enters your house.