What would cause a high-pitched noise in the kitchen?

Answer 1

There could be many causes, only a few of which I can think of at the moment. 1. Failing BEARINGS in any motor [e.g. refrigerator, vent hood, can openrer, etc.]. 2. A loose washer in the sink faucet [but only when in use]. Or water flow somewhere else in the water system [inside or outside]. 3. Very rare, but a misadjusted pilot flame on a gas appliance [range, oven, or gas refrigerator]. For those who are skeptical on this issue, go to any encyclopedia, and study up on "singing flames." 4. A leaking [and "chattering" at a very high frequency] T&P [temperature/pressure relief] valve on a water heater. Like in item # 2, such sound generation can occur somewhere else in a water system, but due to harmonics, not be easily heard in the vicinity where it occurs, BUT be heard at a far distant location [as your kitchen Plumbing].j3h.