it is definately an electronic interference not mechanical sound.
there is a difference in the timing between the two channels too, I mean the two channels were affected with a phase delay but the sequence of the beep is not the same
you can check the attachment where the pulse can be clearly seen.
amplified by 18db and a low cut at ~200Hz showed this.
it was the second clip originaly posted.

You are right. There is slight phase difference in the sample but the pulses are distinct in each channel.

That is a great tool Vasilis. What is that plug-in called? That bright line through the display is the horizontal sync from his monitor. But why different pulses in each channel. I am now thinking induction rather than RF. Crazy stuff.

this is adobe audition's default spectral frequency display (not plug-in).
I'm really confused about the source :-$

Cell phone or monitor, right? I'm banking on cell phone; the frequency of the beeping displays a randomness than does not agree with monitors.

It sounds like a cable or braclet dragging on the boom pole to me. That or a bearing in a fan that is not behaving. If the boom ops heart is going, that pulse could be doing cover the consistancy. Juat another theory.

Confirmed from a shoot last night: it was interference from the boom operator's cell phone.

The moral is to make sure anyone near the sound equipment, the boom operator foremost, has their cell phone turned off.

So, just before every shoot, call him. If he answers.... ;)

Sheesh, you'd think of all people a sound guy would know better!

The second moral is: you get what you pay for. The sound guy was just my friend.

* delurking *

A valuable lesson. In Europe, with GSM, mobile phones interfere with XLR cable runs with a very recognisable cadence.

If you'll all excuse the onomatopoeia, the 'bittly-bip bittly-bip bittly-bip buzz' is the standard call sign of a lonely cell phone as recorded by your sound equipment.

The bangle-jangle 'teaspoon in a glass' is so unlike this that for a while I was going for the analogue outcome, but its regularity and robotic stereo placement are interesting signs to look out for. Great to hear that it's been pinpointed.

Thanks to all for a very illuminating discussion. Lots learned!