Bayer
There is a post I just replied to that may be what your problem is.
There is a small fan inside the fusebox area (drivers side) that may be your problem. It runs when the truck is running and up to 5 minutes after shutdown, same as the aux cooling pump which has been mentioned (same circuit operates both).
If this small fan gets noisy, it usually is described as a high pitched squeeling noise.

Gilly

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