A very weird noise - any ideas?

Howdy folks, I am calling on the brains trust here to help me with a baffling problem I've encountered.

My 1998 HZJ 105 Landcruiser diesel auto is making a random 'WHOOOOOP!' noise from behind the dash on the passenger's side (I kid you not).

It is hard to describe a noise in words, but the best I can do is it sounds like an electrically generated, ascending, 'owl' type of sound. It is not very loud, but still quite audible to everyone in the vehicle.

It happens infrequently at seemingly random intervals, but it is beginning to do my head in. Even my 2 year old daughter is starting to mimic it now.

I have pulled out the glove box, kick panels and centre console but am no closer to finding the culprit. I have been looking for an aftermarket warning buzzer or something similar but with no success. I've also thought about a vacuum hose for the AC controls but have no idea if they are actuated in this manner in a Cruiser. The only other think I thought to look for was an owl's nest.

Accessories I have fitted in the area are an ARB turbo timer, a GME TX4400 UHF, a Belkin iPod cradle and an aftermarket cruise control.

Somebody help me please!