Microwave Makes Noise Like A Geiger Counter

I am asking this question around the web so dont be surprised if you see it elsewhere too

A couple weeks ago my microwave oven started making noises like a Geiger Counter detecting a small amount of radiation (slow but constant low frequency click that is sort of garbled. This happens when it is cooking only not when it is not cooking anything.

I read this on the web so far:

" If your microwave is making noises like a Geiger counter, the sound is coming from the magnetron that produces the microwaves. The sound is normal and there's no reason to be alarmed. If your microwave makes noises when it's in standby that are somewhat loud or strange, something could be wrong with your fan run on. "

But this sound never came out of it before about two weeks ago and i had it for at least 2 years now.
I first suspected arcing but it does not really sound like that, and there is no visible flashes inside as far as i can see through the cracks between the side covers and the front panel.

Any ideas?


Thanks.