Why does the plumbing for my whole house filter produce a buzzing/humming sound?
If your asking what might be causing the sound the first thing to come to mind is a solenoid controlled valve ,but I don't see any in the photo. It may be that it's further along your plumbing system and out of frame. This is common with pipes as the easily transmit sound and vibrations.
It also may be the water traveling through the pipes which does sometimes sound like a hum. This can be amplified by the pipe itself if it is loose and not secured snugly. Air trapped in the line will also cause noticeable odd sounds, but it will eventually get released when a tap is opened.
Sudden opening of valves can cause noises if the water pressure is high enough.
Plastic pipes are also known for not being able to dampen sounds like heavier (metal) pipes do.
Does the U.V. light make any sounds when working? The metal canister on the right edge of the photo.