edit: The noise, when it occured, is a faint 60 cycle hum. More pronounced when you put your ear to the wall where I suppose its amplified.

What is perplexing though, the circuit that toggled the sound is not then one in the room where I hear this?

This not a new problem?

http://ths.gardenweb.com/forums/load/wiring/msg101320165135.html

Here is a link that might be useful: Earlier

Thanks for finding that thread, I couldnt. I posted a new one since I ruled out the light fixture and its acting different than described in that old thread.

So I guess I am confused whether its normal 60 cycle hum, although intermittent as described. I dont think its arcing as the sound is not around any connections that are controlled by the breaker(s) as I mentioned. Also there are no major loads/draw on while this occured nor is there a transformer in the immediate area.

I apologize for the multiple post though, im just confused.

How close is the bathroom to a furnace or HVAC system?

Almost every one of theses uses a 120 VAC to 24 VAC transformer to derive the thermostat controls.

The sound can be easily transferred by metal duct work.

What Is on the two circuits?

A mechanics stethoscope and some time should allow you to track down the source.

Every AC power line has a magnetic field around it (Typical power wiring is NOT twisted for field cancellation, and twisting conductors only works in 'far field' conditions anyway).

Any magnetic object in that field can vibrate form the field.

A single drywall screw that is no longer tight in the wood can transfer vibration to the drywall.

A screw in a junction box that is not tight.

"How close is the bathroom to a furnace or HVAC system?"

I thought the same but the noise did continue with the HVAC circuit shut off.

"What Is on the two circuits? "
Dishwasher and DIsposal in the kitchen where no noise is detected. Neither under load while noise occured.

"Any magnetic object in that field can vibrate form the field."

If it was this, would it ever be transient in nature as described?

Again I would say that makes sense sound wise since to me the sound is similar to say power line buzz, a transformer or some other type of 60 cycle 120 hz hum instead of crackling or sizzling I would associate with a spark.

There is also a 60 Hz electric filed tat can excite any conductor and make it move under the right conditions.

Many (especially new) dishwashers have transformers.

If it was normal 60 cycle hum per say, what would make it occur sometime and others not?

FWIW the dishwasher in question is not even plugged in, in fact there is absoultely nothing as far as I can tell drawing power on either circuit.

Get the mechanics stethoscope and start hunting.

The sound swill get louder ads you get closer to the source.

Many panels have a nice hum around them from the magnetic fields created in the coils used in the breakers.

It is is a hum and not the sharp sound of arcing, it is unlikely to be anything but an annoyance.

I have enough tinnitus to not notice it even in very quiet circumstances without a stethoscope to concentrate the sound.

Perhaps a doorbell transformer is on one of those two circuits?

If concluded this is not from a transformer or motor or any load in question.

Would normal 60 cycle hum from an electrical system be heard intermittantly?

Are you positive it's 60 cycle?
Insects, ie bees, can sound very similar.
Is the sound still present when you shut off the house's main breaker?

A weak connection will produce this also especially on a heavy amperage circuit. If the box or wire is moved it will change tone if that is the case.