Isolate sound to discover vibrating pipe problem

Q: It doesn’t happen all the time, but when my dishwasher runs, I hear a knocking or vibrating sound. It also happens on occasion when my kitchen faucet runs. The faucet is new, and I haven’t noticed the noise at any other fixture. The noise is really bothersome. Help me.

A: We had a customer with a similar problem. She complained of a clunking sound under the sink whenever she ran her dishwasher. When the drain cycle would run, the discharge hose would fill with water, and the hose’s weight would make it bang against the cabinet.

It was a pretty silly job, but the noise really drove her batty.

Your problem sounds a little more complicated. The most logical way to solve it is to try to isolate it.

If the sound occurs only at the kitchen faucet and dishwasher, then they have one thing in common: hot water. That would explain why the faucet only makes the sound sporadically because you’re hearing it when the faucet dispenses hot water, not cold.

Because they have that one commonality, I would start there. It is likely that they share a common water source in the form of an angle valve underneath the sink. Sometimes the dishwasher is on a separate water valve, but I doubt that is the case. Had the noise occurred when the faucet ran cold water, the problem would have been more difficult to isolate.

Usually, with piping noises, we might think of water hammer, a sound that typically occurs when the flow of water running through a pipe is abruptly stopped. This usually happens from an electric valve, such as a washing machine or dishwasher.

Electric valves stop the water so quickly that a shock wave travels the length of the pipe until its energy is used up. That can result in lots of noise and frustration. Water hammer doesn’t usually happen from a manual valve unless a person really slams the handle down hard.

In regard to your vibrating noise, as the hot water is the commonality, I would surmise the problem lies with the angle valve under the sink. The valve probably has two nipples that supply both the dishwasher and the faucet.

My guess is that this valve either has a piece of debris in it — maybe the water company was performing work in the street and some debris found its way into the supply — or more likely, a washer in the valve is loose and, as water flows, it squeals like a pack of fans at a pop music concert.

First, turn the water to the house off and disassemble the supply hoses from the valve, then remove the packing nut and pull out the stem.

You may notice a little pebble or some other debris when you remove the stem. If so, you have found your problem and can reinstall the stem.

The most likely culprit is the washer. As you rotate the handle of the stem to open and close the valve, it moves the back of the valve in or out. What seals the valve shut is a washer at the rear of the stem, and a tiny screw holds the washer on. Inspect the stem and see if you need to tighten the screw, replace the washer or even replace the valve.

All parts are readily available at any home center. When you put the valve back together, wrap the threads with Teflon tape to prevent drips.

Mike Klimek is a licensed contractor and owner of Las Vegas Handyman. Questions may be sent by email to handymanoflasvegas@msn.com. Or, mail to 4710 W. Dewey Drive, No. 100, Las Vegas, NV 89118. His web address is www.handymanoflasvegas.com.