Phew! I was beginning to suspect that DROBERTS thought I was bonkers!Or sometimes finding a bit of bone behind your ear can work well. I used to have one of those old fashioned wooden screwdrivers with a long metal shank and a round wooden handle. If you rest your skull against the wooden handle and the other end against the component that might be making a noise or vibrating you can hear the offending sound very well.
A listening stick is just that, a stick for listening! Usually a hard wood dowel about 1cm diameter. (I'm guessing a bit here) You press it against the side of your skull, just in front of your ear. The other end you press on where you suspect a noise is coming from. You can track down the source of a noise. They are particularly effective for subtle noises like yours. I presume you've tried to freewheel out of gear to compare the noise with gearbox engaged, in order to eliminate a road wheel bearing etc. You might need to get it up on a four post to listen to the transfer box in action with the stick.
Well, just to give an example. If I'm having a bath and put my watch on the side near the taps and then lie down and rest the nape of my neck on the back of the bath I can hear it ticking. The vibration comes all the way through her bath and the back of my skull. I've got to be quite close up to hear it under normal circumstances.