Just my 2 cents...I get a noise in the same area and when I put the fan on the noise goes away. My son says it sounds like a popcorn popper. Brought it back to the dealer but of course I am crazy and hearing things - you know the routine. I have to stay away from the service manager otherwise bad things might happen to him.

I was thinking the fan motor is under there and going bad. Like I said everytime it happens, I just turn on the fan one notch and it magically disappears. Now i am waiting for the noise to become more constant. Once that happens i will buy the part and fix it myself.