I just tracked it down to a bad window switch. I was suprised as they never seem to go. I took the whole switch apart & did not see any evidence of a bad or burnt board, prob a bad hardware chip.

If yours is dropping in its own I would suspect the regulator is starting to go. Mine never dropped on its own it just was stuck up.

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01 X5 3.0 / 04 Volvo S60R 6MT/ 91 Corvette 383