Crackling/"Rustling" sound in 300M

While driving at freeway speeds today, I could hear an annoying noise in our '02 Chrysler 300M -- like rustling leaves, perhaps, but loud and
constant.
Turning off the fan didn't seem to make any difference. When the car was not moving, there was no such sound, even when I cranked the fan up to its highest speed.
Are there ventilation ducts that could have an accumulation of dry leaves and are independent of the HVAC controls? If so, any ideas for dealing with the problem. And please don't tell me to pull the whole dash apart: once was enough for a lifetime.
Or is there any other possible cause?
Perce
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Percival P. Cassidy wrote:

You think the sound is in the cabin air-handling system?
Or could it be suspension / wheel-bearings?
Brakes? Maybe a caliper is not releasing the pads? Are you sure the parking brake (emergency brake) is not engaged?
You get this with the hvac controls set to OFF?
Next time, try setting the ventilation control to cabin-air recirculate mode. That tends to always turn on the compressor for some reason - I think to de-humidify the recirculating air. But the recirc mode does seem to close off some doors in the ductwork so that should make some difference if the sound is being caused by something loose in a duct.
I don't believe I've ever heard that sort of sound in my '00 300m.
The one thing I have got to do with my car is flush the heater core. I'd love to replace it, but taking the dash apart to get to it is just way too much work from what I can see in the service manual.
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On 12/23/2017 10:41 PM, MoPar Man wrote:

Thanks for the suggestion about the a/c controls. I'll try that.
Perce
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