2003 X5 (Aux?) Fan Keeps Running

Could anyone suggest a reason why the auxiliary fan in my 2003 X5 keeps running even after the engine and ignition are shut off? I presume it's the
auxiliary fan but don't know for sure. The fan noise is emanating from the area where the cabin filter is installed under the hood near the firewall. Is it supposed to run all the time?
Tonight the fan sounds as if it's running at a constant speed. On other occasions (last night, for instance) it sounded as if the speed varied. This observation is based on the pitch of the fan sound. It appears to keep running for hours after the engine and ignition are shut off. The car has been off about 3-4 hours tonight and the fan is still running.
There doesn't appear to be any way to get it to shut off. Last night I started the engine, turned off all interior fans, then shut the engine off. The fan noise continued for several minutes (variable pitch noted) then stopped. I tried the same thing this evening with no luck.
A Peake Research scan tool reported no codes.
The vehicle is out of warranty, so any help would be appreciated.
Thanks in advance!
~ Dave
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This could be normal operation. The electric fan comes on when the cooling load is high. As you appear to live in Florida then this could be real. The fan will run for a minute or two after switch off (wired round ignition) if you have been taking a lot of power from the engine or idling a lot (e.g. towing, hill work, just come off freeway or sat in traffic for ages).
If it is staying on all the time or long after switch off then probably the thermal switch for it needs cleaning or replacing.
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Is your X5 equipped with the programmable forced venting system? It is used to turn on the fan and vent hot air out of the car before you plan to get in it to drive. If so, perhaps you have inadvertently programmed it to turn on.
Eisboch
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I don't think it's your radiator fan running. You indicated the noise is coming from near the firewall. That's why I think it may be your forced venting system, if you have one.
Eisboch
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R. Mark Clayton wrote:

3-4 hours running is definitely not normal.
--
-Fred W

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Indeed 3-4 minutes would be normal.

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