Clocks just changed in the US so out in the dark more often. Put on the interior roof center console lights in my 2010 XF SC this evening. The one in the middle makes a high pitched humming sort of noise when it's on. The ones on the left and right are silent. Any ideas? It's a standard filament bulb, I haven't done leds. I doubt there is a transformer. What else could it be?

Will change the bulb and see if that fixes it but other ideas welcome!

 

Since they go on and off with a gradual on, gradual off operation, I suspect what you are hearing is buzz from the PWM circuit that does the dimming. It is probably just a squeaking inductor and whilst annoying, probably not going to fail anytime soon.