Source of 60hz-ish electrical hum?

While trying to connect wireless speakers for the Xmas season I noticed that on the receiver end I get a distinct hmmmmmmmm. I tried different plugs and turned off all the fluorescent lights I could find. Still there. Also I don't think any appliances and/or chargers were functioning at the time either.
Can some of you please suggest what other areas I might check?
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Yours or neighbors cordless phones and equipment can be an issue, is it 900mhz, alot of things use the standard frequencies, outlet wiring and ground can have effect, try turning off all breakers to see if you can isolate it, is it a wide plug that goes in one way, reverse the polarity, you have to experiment, or maybe the hmm is a defect, take it to the neighbors and try it.
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Bob M wrote:

Probably a leaky power supply. Or a really cheap one.
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Some wireless speakers aren't designed all that well, and suffer from the very problem you describe. Even good models, as they age, begin to suffer this problem in some cases. The electrolytic capacitor(s) used to filter the power supply get dry and provide less filtering. Can you try running them off a battery supply or a known good source of DV to see if they still have the problem? This would separate your problem as being either "conducted EMI" versus "radiated EMI". Conducted comes from the power line or power source / power supply whereas radiated comes from fluorescent lighting or other nearby sources of RF interference.
Smarty
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First connect wired speakers to your receiver and check for a hum. This is a common, but tricky to diagnose, problem in audio systems. If your amp has a hum that is heard through wired speakers, it is a ground loop problem. This is caused by multiple groundings. Only one source of ground is recommended as a loop is formed when multiple items are interconnected while plugged into grounded outlets, this includes the grounded sheath of "cable TV" cabling. Only the amp should be grounded all other equipment should not be grounded. A grounded "cable TV" cable may need an isolation device added in line with the cable.
If you have no hum through wired speakers, then it is the wireless system picking up the hum or the circuitry is creating the hum.

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Light dimmers are a possible source.
It's also possible the origin, whatever it may be, isn't even on your property.
Old wireless 'AM' intercoms were notorious for picking up 60Hz hum's.
Good Luck,
Erik
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