faucet whines when hot water on

I have a 2 1/2 year old house with PEX plumbing. Starting about 6 months ago, whenever I turn on the hot water on the kitchen faucet a (fairly loud) mid-pitched "moan" or "whine" starts. It doesn't start until the hot water has been flowing through for several seconds, and continues even after I switch to cold water only for several seconds, then goes away. If I only use cold water I never hear anything.

So far all I've tried is to take apart the faucet and clean everything, replace the screen, etc. but to no avail. I'm not much of a plumber, so does anyone have any ideas?

There's a part in the faucet or a valve somewhere that vibrates. It shouldn't. The trick is to find it. If it only happens when you use this valve, then that's probably where the vibrating part is. It could be in a stop beneath the sink or in the faucet itself.

In the old days, the most common cause of this was the threads in a seat and washer faucet - as you turn the handle back and forth thousands of times, the threads wear and the space between threads allows the stem to vibrate. Or it could be a loose washer or something.

If there's a stop beneath the sink, open it or close it a little and see if the vibration stops.

If you can, try replacing the stem with a new one.

We had the same thing happening - in our case it was the bypass valve on the water softener. It wasn't being used so I just closed the valve and it stopped.