Nail Pops Galore

I've lived in my '57 ranch for about 4 months and, within the last few weeks, started noticing SEVERAL nail pops in the sheet rock. The nail pops are located on almost every wall and ceiling in the house - mostly up high but not exclusively. In total there are probably 75-100. I noticed a few here and there when I bought the house but since the weather changed I have noticed them appearing everywhere and have become very concerned. There are two possible causes I can think of: - A few months ago I knocked out a wall and put up a header (12' span) on an a former exterior wall to open up the kitchen to the room addition. - I also had the gutters off for a couple months when replacing the siding. Any ideas on the cause(s) and/or ideas about how to solve the problem would be greatly appreciated. Thanks!