Shower faucet help needed - humming/vibration

[Sveedy]

With your shower diverter, the line that goes up to the shower head should give the necessary cushioning.
I hope you know what your getting into when it comes to installing your new unit. You will have to open up the wall behind the shower
( hope it's in a closet ) and cut the old one out. Then, assuming its copper,sweat solder your new one in. You can use unions in some cases, but I prefer to solder as much as possible.

[matthew1]

I don't think I need to mess with pipes because the hot/cold blend is done in the cartridge I posted a photo of. The big hole is cold, and the two others are hot. I'm crossing my fingers this is what's vibrating, and a new one will fix the problem.

[matthew1]

No scratch that. The two smalls are hot/cold, and the big is output.

[Sveedy]

I misunderstood. I thought you were getting a whole new valve.

Carry on...It should all work out ( famous last words ).

[matthew1]

Part came today, and it wasn't the fix. Any thoughts?

[matthew1]

The water heater is around 15 years old. Could that have sent up a piece of debris into the hot pipe? Hot on that faucet doesn't run as fast as it used to. It's about half flow.

Hot works normally elsewhere.

[Sveedy]

Well that's a drag. And kind of strange, it just starting like that. I know that my water pressure seems to vary a little according to what else is being used at the same time, such as the laundry. I had a underground leak one time and that's how I noticed the problem. But I'm on a well.
I don't think it's a piece of stuff from the heater. I don't see something making it all the way from the bottom of the tank, up the outlet tube and along to the valve. But I'm no plumber ( obviously ). You could try to flush out the pipe but I can see a mess doing that.
Is this valve right in line with the water heater ?

[Sveedy]

In your sprinkler line thread you mention having the lines blown out. Why ? Did you have a water line break by any chance ? If so then look in your toilet tank and see if any dirt etc is in the bottom.

[matthew1]

In your sprinkler line thread you mention having the lines blown out. Why ? Did you have a water line break by any chance ? If so then look in your toilet tank and see if any dirt etc is in the bottom.

Underground sprinkler systems must have that done every fall because winter will freeze and break the pipes.

No sediment in the toilet tank. The hot pipe meanders here and there before routing up to the bathroom shower. It's a 1926 house. All the water pipes are copper, but I don't think they're original.

[matthew1]

It's gotta be something clogging the hot pipe to the shower. But the noise/vibration is weird. Maybe that's just natural to a clogged system with a mix valve.

Cold: full flow, cold water
Midway: reduced flow, lukewarm water (normal), noise/vibration
Hot: half flow, hot water