Sorry you are right I thought they were in the package tray till I looked at mine.

 

I'm glad I finally zeroed in on the general location of the noise source.

But we are still barking up the wrong tree.
Can't be the gas tank opener/lid.

Can't be the velcro/tab or gas tank manual opener (pink). If it was, the noise would be regular.
It wouldn't start spontaneously and then stop and might not start again for weeks!

We are going to have to put on our thinking caps and think rationally.
Can any of those wires in that cable bundle emit noise when a signal is given?

I have power adapters that emit noise (hissing) through its coils.

 

Wires not in this case being wound with others to dampen any harmonics by vibration. Buy a cheap mechanics stethoscope from a place like harbor freight to pinpoint noise location. Start at the seatbelt box. I don't know what is in there but could be something electrical.

 

Thanks alextv.
I'll be buying a stethoscope.

 

Try putting something in the left back seat where seat belt can be pulled and buckled just to see if any difference. Have read where the tensioners can cause a tapping or clicking noise.

 

Thanks.

I started by buckling the back left seat and then I tried some experiments which were very interesting.
These were done with the seat belt buckled.

First I just pulled the belt out as far as it would go and it made a clicking sound, but nothing like the noise I'm trying to stop.
Then I released the belt (it retracted) but didn't make a noise while retracting.
Then I pulled the belt out again. This time it was the reverse!
It was silent when I pulled it out but when it retracted it made the clicking sound.

Very strange.

 

NoiseFree - Any updates on tracking down your Geiger counter noise?

 

Thanks for asking JRB.
I was just going to post a followup.

I did buy a mechanics stethoscope last month. As was always the case, the noise went away for a few weeks and came back again the past week, including
yesterday.
I keep the stethoscope in the trunk where the noise is and rush out to the trunk to listen if I have the opportunity to stop the car in time.

Yesterday I still couldn't trace it. I listened at to the seat belt terminal of the back left seat belt but that's not where the noise is coming from.
I also have pulled the cover from the back left side of the trunk (where the noise is coming from) so that it is loose and I can retract it to get inside there.
But so far I'm at a loss as to where to listen.

I do know that the sound is coming from the left side (driver's side), inside the trunk.
I suppose that is progress from when I first started. But I still haven't located the source and
it really is bugging me.

I'm still open to suggestions here as to how to proceed.
One of the biggest problems is that not only is the noise intermittent over a period of days/weeks,
but also when it starts it can continue sometimes for 20-30 seconds and then stop.
Or start and stop sounding for only a few seconds each time.