Transformer is Buzzing - Unsafe?

I have a 9VAC GE security system transformer that began to make a faint buzzing sound and I'm worried this may be unsafe. The noise started a week ago after several weeks of it *not* buzzing when first installed - or at least I never noticed it. The unit does *not* appear "hot".
I changed the receptacle that it is plugged into and checked for grounding and it is properly grounded. I tested the voltage for 110v with a multimeter and it is steady at 110. I also swapped the transformer with a new one but it still buzzes. Finally, I ran the transformer to another two outlets and it buzzed on both, but each with different intensity.
What could be the cause of this, and how do I fix it? Is this a warning that it should not be used or corrected?
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Hi, Unless it is unusually hot to touch, I won't worry about it other than annoying noise. If it is expose tranny with metal cover, try to tight the iron core lamination. Tony
Billy wrote:

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It means parts of it are loose and rattling. Most of the time the only problem is not noise, which may get worse with time.
If the noise is a problem, or it starts getting warmer than usual, replace it.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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What your hearing is a transformer core lamination vibration.
When these transformers are assembled they are usually dipped in a electrical varnish. This would intended to protect the winding but also seals the thin metal sheet metal of the core laminates.
You didn't hear the buzzing early on because the varnish was still sealing the laminates. After a time, it sounds like some of the laminations have broken the bond of the varnish and are 'humming' the 60 hz tune.
If the transformer isn't over heating then the insulation of the windings is probably still doing it's job.. If you can live with the noise, I wouldn't worry about it. If it's annoying you, contact the OEM and ask for a new transformer.
Steve
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I had two of them checked out by an alarm company on two different houses recently. Both alarm systems had been installed about 3 years ago. The alarm service company -- which was not the same company that did the installation -- said it's nothing to worry about and it's very common. They said they could replace them for me if I wanted, but that I'd be wasting my money. On one, they just tightened the mounting screws (I think) and the sound was reduced but still present.

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Actually if they replaced then with quality transformers, it would be unlikely the problem would return. Most transformers are really cheap.
--
Joseph E. Meehan

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