Whirry noise from behind Odyssey dash

Our 2000 Odyssey (with about 97,000 miles) has begun to make a slightly irregular light-rattly whirry noise which seems to come from behind the center point of the dash board. Happens with or without AC, with or without heat, with or without fan. Sort of a “fla-fla-fla-rattle-fla-fla” noise. Noise began this summer and has continued into the fall. (The car does not deign to recreate the fla-fla noise when it is in the shop. Had it to two places with no luck. (Have the sound recorded, which I brought to the dealer, but they couldn’t/wouldn’t play it for the actual people working on the vehicle.)

Just before the noise got going, the car also started having problems with the electronics to the radio/CD player – but only during the warm weather: the CD player/radio would periodically continue to play for maybe 10 seconds more after turning off the ignition which is supposed to cut off all juice to the thing.

Additionally, gas mileage has dropped considerably from about 18.5 mpg around town a year ago to 17 mpg in September, 15.5 and 14.5 mpg in October and now to 13.5 as of my last fill-up 11/24. While I’ve had to make many more short runs this year than last, that doesn’t explain the constant decline.

Any idea what the fla-fla noise could be? Is it likely related to the electrical problem? Are either or both related to the gas mileage drop? Or has built-in obsolescense just set in?