Bad Problem with solenoid valve.

Some helpful videos in the link as well as text articles and a link to a previously answered question on Fixya.

https://www.google.com/search?q=Aprilaire+760+making+strange+sound

It may be too high a water pressure for the solenoid.

Aprilaire Humidifier, too powerful a solenoid? Vent ducts noise.

https://www.houzz.com > discussions > aprilaire-humidifie...
The noise might be caused by having the water pressure up too high for the solenoid. Try backing off the water supply until the sound goes away. Hopefully, ...
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The solenoid is going bad and might start a leak later if not fixed or likely won't stop the water flow! Get it replaced!

It's not uncommon for duct work in an older home to Bang as the furnace cycles due to age. The humidifier banging while turning on and of is mostlikely the solenoid valve; if the solenoid is bad it is actually to your benefit to replace the entire humidifier as the solenoids are very expensive, 50%+ of a new humidifier. Plus you get the 5 year parts warranty on the new unit instead of just one year on the solenoid. If you don't want to replace the entire unit you can replace the Humidistat, and that should fix the on/off cycling, however a new humidistat is included with a new unit, which again is more cost effective. They are easy enough to replace as a do it yourselfer, especially when replacing an existing unit. I hope this helps you.

Hello, usually a ringing or buzzing sound comes from the solenoid valve on the humidifier. Make sure that the solenoid valve is getting a solid stream of water to it, sometimes if there is not a good stream of water the solenoid will buzz. if that checks out good than replace the solenoid vlave.

Check to see if you are getting 24 volts at the transformer, if you are then bring the power directly from the transformer to the solenoid valve and see if the solenoid valve clicks open by moving the knob on the humidistat. If nothing happens then most likely the solenoid valve is bad and needs to be replaced. If the solenoid valve does work after bringing power directly to it then either tne problem is the humidistat it self or the sail switch/current sensing relay.

The water solenoid valve in your Aprilaire humidifier makes an audible sound anytime it opens and closes. This is normal operation. On occasion a mineral deposit may become lodged in the valve. When this occurs the valve may make a buzzing sound as the plunger is not seating properly. You may dislodge the deposit by lightly tapping the valve.

Thank you for giving us the opportunity to be of service
Sincerely,

Brad Uselmann
Technical Support
Research Products Corporation

www.aprilaire.com

A bad circuit board should not make any noises. A bad solenoid valve could make a loud buzzing noise. If the noise is a squealing noise then you have defective bearings in the blower motor.
If you disconnect the low voltage wiring from the solenoid valve and you still hear the noise, then its not the solenoid valve.

We recently had the same problem. After cleaning both the furnace filter and the humidifier water panel, the clicking noise (electric air filter) and the loud bang went away.

Try turning the water valve going to the soleniod down. There may be too much pressure. You may have to replace solenoid one more time after making the adjustment.

Not sure what type of humidifier you have but if is a power humidifier like the April 700 or 760 they do have a blower motor and it may be the fan blade is broken.But if you have a bypass humidifier is posible that your water solenoid may be making noise because of to much water pressure there is not much to a bypass humidifier, you may want to close the water supply valve a little at a time se if the noise goes away.