Our best guess is water got in there during a really bad winter but I'm not sure of that. The whole back side of the house has bulges where the nails have come out and the siding is pulling away from the house. At this point, since it's so pervasive I think it's best just to remove the siding completely and basically reinstall it. Would this work, would I run into issues doing this? I've noticed there is foam insulation under the siding too which doesn't appear to be attached well, I'm wondering if the original nails were not really long enough to go through that and into the sheathing.