You might want to try a trick called, " Lifting the ground".
I've had some hums and hisses before when I had my reference monitor plugged in and connected to my xh-a1.

If you have any other items plugged into your camera, unplug them one by one until the hum goes away. If you find the culprit and it has a 3 prong plug then go to ace hardware and buy a 3 prong to 2 prong adapter and use that to plug the device in. The adapter basically removes the ground loop that could be causing the feedback or hum.

Great sound guy taught me that once and it's saved me on several occasions.

Jay,

I also find it odd that the hum disappears when you plug in the wall power and disappears on battery. Like you, I'd expect the reverse to be true. I cannot wrap my brain around any reason why this might be happening for you.

I think you might want to eliminate the rental microphone as the source of the hum. You could take your kit to the rental house. Explain what's happening and see if they'd let you test some other mics. I think they'd want to know if their mic was faulty.

Scott -

Thanks for the tip - I don't have any external components attached right now, other than the mic and my headphones. However, I will have to remember that for future use...

Tripp -

I think I am going to do that if I can find some time to get down there. Unfortunately, it will take about 2 hours round trip due to traffic, etc. Maybe I an cut out of work early today...

In the meantime, I posted a sample of the hum on youtube:

YouTube - XHA1 hum

It is fairly quiet to me - I have to use headphones, or turn the volume up fairly high to hear it. Of course, the power supply on my PC is fairly loud, so it may be more obvious to those with quieter computers...

Jay,

unplug your pace-maker! just kidding.

Have you tested the setup in the same place every time....have you taken it outside and tested?

I had a hum like that and it was being caused by rf from a ballast.

I'm just shooting in the dark for ya...so don't stand too close to me.

Sounds more like vertical refresh rate spatter than traditional hum. That it changes with LCD orientation makes is sound as though there is a cable or connector that is loose, stressing, or changing position when the LCD panel rotates.

Back a number of years ago with an XL1 I encountered a situation whereas with certain brands of battery there was an increase in nose when using the MA100 XLR adapter. Probably related to the details of the battery internals. But I do not recall all the details at this point. If y0o can try different batteries to see it it changes.

Also, try beg, borrow a different mic, even a cheap XLR SM58 wanna-be from Radio Shack, to se e it it exhibits the noise.

Could hear the noise in the UTube post, but not sure how to down load a bit of the audio so I can look at the frequency spectrum and waveform.

LOL! Come on, I'm not THAT old :)

I have actually tested in my office, in my living room (where I first discovered the issue), in the garage, and finally, today, with the mic in a closet and my camera in my office. It has been too windy and / or rainy to test outside... Maybe tomorrow - the neighbors might think I'm nuts if I am outside recording in the dark...

Thanks for the feedback, Don - one comment though - I get the same results by turning on the EVF from the menu, so it's not really dependent on the LCD position - it really boils down to whether the EVF is on or off. It just so happens that the easiest way to make the problem appear and disappear is by moving the LCD...

The battery comment is interesting, because as I stated yesterday, I do not get the hum when running off of AC power. I would not be surprised if there is a voltage difference between AC and battery, and maybe that is the problem. It would kind of make sense, when I think about it, as I would normally expect more noise from AC power. Maybe AC provides a more stable current under load? I'm afraid I am getting out of my league on that topic though...

I plan on going back to the rental place tomorrow, if I can get away, to see if they will let me test another mic. I will post an update some time tomorrow evening...

Any further progress on addressing this issue?

Hi Don -

Not yet, unfortunately - I've just been too busy. Between the hours at the rental place and my hectic daytime schedule, I am hoping to get down there on Saturday now. In the meantime, I'll be using the mic on Thursday, so hopefully my workaround won't fail me...