My husband and I bought a 100 year old house with a claw foot tub about a year ago. Last week I turned the hot water in the tub on full blast it filled the tub about 2 inches and then began knocking loudly and spitting. When I turned the water on at a lower pressure everything was fine. I slowly turned the water pressure up; at about halfway to full blast the knocking and spitting began again. More information: This happened with both hot and cold water when turned on independently and/or together. The hoses coming up from the floor that connect to the back of the tub shakes violently. The tub seems to be the only thing affected by this. The water in the sink and toilet in the same bathroom can be run at full blast and are unaffected even when the tub is spitting and banging. This is our only tub/shower, but water running in the kitchen sink, dishwasher, washing machine on full blast/high pressure are all fine. The knocking/banging is very loud, tub is on the second floor and can be heard throughout the first floor and basement. When I went to the basement the copper pipes coming out of the water heater shake when this happens but seem to shake less violently than the hoses attached to the back of the tub. I turned on and off the water at least 20 times, this happened every time.

I gave up and went to my parent’s house to shower. The next day I turned on the tub, full blast, it was fine. For several days everything was normal, we filled the tub and showered without incident. Last night I began filling the tub and again it started loudly knocking and spitting. I turned the water on and off about 10 times, again trying to figure out what the heck was happening and why, and on the 11th try or so it stopped. This seems to happen without warning and correct itself, at least temporarily, randomly.

I do not have any plumbing knowledge but I imagine that if something was wrong with the hot water heater or the main lines it would affect more than just one tub in my house. While I would like to imagine that I corrected the issue by cursing the faucet, the previous owners, and home ownership in general, or simply by willing the hot water to flow, I sincerely doubt that the issue is corrected. Instead I fear this issue is lying in wait to pop back up when I need to shower most. Any ideas?

Sounds like loose washers in the faucet. Dissasemble the faucet handles and stems(make sure water is off to house when doing this) then you should see a washer at the end of the stem that is secured by a screw, tighten the screw and let us know if it solves the problem.

Does this knocking occur using shower or filling tub or both. Since it occurs both hot and cold I'm thinking loose washer in diverter valve. You do have do have a diverter valve on the wall don't you.

I agree with Lee.
It sounds like a loose or broken washer. Follow his advice,
dissasemble the faucet handles and stems(make sure water is off to house when doing this) then you should see a washer at the end of the stem that is secured by a screw, tighten the screw I've put up a image to help you. Before you button things up turn the water back on to flush out the supplies and any debris that may still be in there. Good luck, Tom