I can run my kitchen hot water at a low flow, but if the flow is anything more than a low flow, it stops flowing with a "machine gun" sounding rattle in the pipes before it completely stops the flow- it actually sounds like some sort of check valve in the hot water line rapidly opening and closing. If I quickly turn on the hot all the way, the water shuts off immediately or keeps a slow flow with a persistent "machine gun" sound - I can actually see the pipes vibrate under the sink when I do this.

When the flow has stopped with the hot "on", when I turn it off I can hear something release - again, almost like a check valve. All of this weird activity does not happen with the cold water flow and it does not happen with any other hot water flow in the house.

I replaced the faucet thinking the old faucet was gunked up internally and causing the problem - but it's still happening with this new faucet, and even seems worse. The old faucet was a single handle faucet and this new one has separate hot and cold handles.

What gives? I have not idea what would be causing this.

Could be a problem with the stops under the sink.

Did you replace the supplies from the stops under the sink to the new faucet?

These are generally only 3/8 in diameter, and a blockage or partial blockage in these can lead to hammering.

A blockage in the stops themselves can also lead to hammering.

If you re-used the supplies, buy new ones and flush them into a 3 or 4 gallon bucket before connecting them to the new faucet.

If you have hammering while flushing the new supply lines, then you might also consider replacing the stops.

Be fore-warned, though, if you have galvanized plumbing, and I suspect you do, the threads on the nipple your stops are attached to may break off when you try to remove the stops.

By "stops" do you mean shut-off valves? I don't have any shut-off valves on the water lines under the sink (it's an old house with a lot of "Handyman Tim" work done in it before I bought it). My flexible supply lines connect directly to the copper water lines under the sink. I think the flexible supply lines under the sink are newer- I'm pretty sure I replaced them a few years ago when I put in a new faucet, but they could have some gunk in them I suppose.

If I read your suggestion correctly, you are saying 1) get new supply lines (maybe adding shut off valves would be good too, huh? ) and 2) flush the hot water line for a minute or two before hooking it up to the faucet. This would get rid of any blockages and flush out any gunk that might be sitting in the line.

Did I get that right?

Thanks for the insight.

Wat you have is called "chatter" in my area. This is caused by a obstruction in the line or faucet vibrating and the water rushes by. As you've changed out the faucet we can discount that. When you changed the faucet did you also flush out the supplies? If not you should have. Growler hit the nail on the head when he advised you to check the supplies. I wouldshut the hot water off at the heater and open up the cold water side of the faucet and see if it chatters. If not then the problem's in the hot water supply. As growler has suggected. Flush out the supplies. Regards, tom