I have this exact same problem...although its actually air escaping from between the hard top and the frame. If I stand out side I can feel the air escaping with my hand.
When you roll the window down it relieves the pressure and the noise stops.
If you wheel your bronco often, you should NOT (if helped) be rewelding the stock brackets, yo SHOULD be looking for heavier 1/4 IN aftermarket brackets and stop playing around with the OEM stuff.
https://barnes4wd.com/collections/ford-bronco-suspension-brackets
Although it doesn't get that cold here in Southern Arizona, I have noticed once its 40 degrees or cooler, I get a whistle noise from the drivers side middle panel. Its mostly on remote start, once I hit the push to start it goes away.
If I stand out side I can feel warm air rushing from the...
I actually removed the panels and reinstalled the other day and it seemed to fix the whistle but it came back, I didn't notice this particular area, but I thought it might be folded over but I cant really tell with it on, so probably need to remove again.
I tried searching the interwebs on this and it seems it has happened to to other folks, some saying its "normal" but I do not buy that. Recently I started having a "whistle " noise from the drivers side behind my head either at highway speeds or sometimes when the AC is on with the fan speed...