ProMonitor 800 Resonance

Magnetic resonance imaging (MRI), also known as nuclear magnetic resonance imaging, is a technique for creating detailed images of the human body.
The human body is mostly water. Water molecules (H20) contain hydrogen nuclei (protons), which become aligned in a magnetic field. An MRI scanner applies a very strong magnetic field (about 0.2 to 3 Teslas, or roughly a thousand times the strength of a typical fridge magnet), which aligns the proton "spins."
The scanner also produces a radio frequency current that creates a varying magnetic field. The protons absorb the energy from the variable field and flip their spins. When the field is turned off, the protons gradually return to their normal spin, a process called precession. The return process produces a radio signal that can be measured by receivers in the scanner and made into an image.
What is an MRI Magnetic Resonance Imaging

There will be a section of water pipe which resonates to the vibration the water causes when in use. Find that section, quite possibly a 3 or 5 foot section not fully secured by clips. The cure is to alter the resonance, bit like a guitar string, by fixing the pipe to a solid surface, even a wedge may do. OR find out which tap is on when the water hammers and replace the washer or gland. Sometimes it is trial and error to alter the resonance frequency

pots are broken, something fell against them, they need to be replace. Shop time

This might or might not be your problem, or the fix, but if you have a set of wrenches and sockets, it won't cost you anything.

I had a bike that would "drone" only when the engine was running at 2000 RPM to 2300 RPM.

It turned out it was a loose exhaust pipe mounting.
Not so loose that I heard a rattle, but rather "Mechanical Resonance" (here's a "cut and paste" definition - "Mechanical resonance is the tendency of a mechanical system to absorb more energy when the frequency of its oscillations matches the system's natural frequency of vibration than it does at other frequencies. It may cause violent swaying motions and even catastrophic failure in improperly constructed structures including bridges, buildings, trains, and aircraft. When designing objects, engineers must ensure the mechanical resonance frequencies of the component parts do not match driving vibrational frequencies of motors or other oscillating parts, a phenomenon known as resonance disaster.")

So go over EVERY nut and bolt you can get to and see if any are loose, and tighten them if found, and try it out.

Check the tachometer while changing from from neutral to drive; you should see a change in the RPMs. Rattles have a resonant frequency and the minor change in engine speed may be causing it to reach resonance, making the rattle more apparent.

The noise MIGHT be a resonance in the cabinet. The way to find out is to sweep a frequency upward to see if something rattles at certain frequencies... Don't be surprised to find several. Within the cabinet are the usual culprits: Wires rattling against the cabinet, loose debris, grilles and the logos on them, circuit boards with crossover hardware, cabinet wood that is not glued and rattles against itself. Things like bass port tubes can rattle.
Find an audio generator and sweep the cabinet from 50Hz to 10KHz and you will be surprised. Some speakers may have resonances as well. Expect things in your room to start rattling as well.
This is really the only way to find the problem. PLEASE wear hearing protectors at levels above 90Db.

Many people believe that a powered subwoofer is only necessary if you are using small bookshelf speakers. While a powered subwoofer main purpose in home theater is to reproduce the Low Frequency Effects (LFE) channel. This channel (the ".1" in a "5.1" or "7.1" recording) was introduced with Dolby Digital and DTS and offers a completely unique conduit for low frequency information and effects.
The LFE channel dramatically improves the impact and emotion of scenes in all types of movies. Imagine missing out on the resonance of the approaching T-Rex in Jurasic Park, not feeling the rumble of an earthquake, or missing the low tone that penetrates your body just before the bad guy jumps out at you in a scary movie. Emotion is often conveyed through a movie's soundtrack and a powered subwoofer makes the most impactful low notes really hit home. Invest in a good powered subwoofer- you'll be glad you did.

Does the lit gas vary in amount of flame ? Are the gas jets clean?
Is the autovent screw opened at least 1/2 to 1 turn?
Possible resonance within the boiler casing - press and hold side & front panels to suppress the resonance frequency

Could be one of your wheel bearings going bad- I've had to replace three of the four on my 2002 S-Type in the last two years. Raise each tire off the ground -- if you can wobble the tire with your hands, the bearing is bad. They shouldn't move at all if they are good.

I've had the same problem/s. A manufacturing fault with the original midrange drivers of all of my Mission 780's and 782 speakers. If you contact Mission through their website they will supply an updated style driver for about £45, I would recommend buying 2 because the other one will fail eventually, if like me you use them every day. All four failed within two years of each other.

Regards

kingar