Howdy folks. When I turn my shower on, I have to turn the water all the way to hot, switch the shower lever, and then adjust to warm... otherwise I get a huge loud knocking sound from the basement. I went down to see if I could see pipes rattling or anything, but nothing. I turned on the faucet of my utility sink down there and the noise stopped. Any idears how to fix or what's the cause?

Thankee!
D

One handle or two knobs? What's the brand name of your tub/shower valve? Does it make the noise when you run a tub or just the shower?
Until I know more about what you have I can't be of much help. More details
Please. Regards, Tom

It's a single. Its when the tub faucet runs. I think it may be a kohler... its fairly new. Thanks! Please let me know if you need any additional info.

Several things come to mind. It could be the flap in your diverter that's vibrating or it could be a small piece of mineral build up or a tiny pebble that vibrates against the valve body inlet as the4 water rushes by.
I would shut the water off and open up the valve. Then I would turn the water back on and flush out the supply lines. Now try it. Good luck, Tom

Thank you very much. I have no plumbing experience, but I will try what you said. Alsol, I mentioned it was a knock, but really its quite a roaring knock, if you know what I mean. Very loud vibrating noise... very fast like a machine gun.

Any further thoughts are appreciated.

A few years ago, I had a noise like that when my washing machine started to fill. It turned out that an upstairs faucet on the same supply line had a very slow leak. When the leak was fixed, the noise when away. I've wondered if air might have been sucked back through the leaking faucet when the washing mahine valve opened creating a loud hammer/vibration type sound.