Okay, I know someone here will know the answer to my question.

I'm looking to hang some shelves/cabinets on the interior of an exterior wall. That is to say the cabinets would be mounted inside the house but the other side of the wall faces the street. For the life of me, I cannot locate the studs. The stud finder doesn't pick up anything. The only studs I can positively locate on that wall are on either side of a window. I used a strong magnet to locate the screws used to fix the dry wall to the studs. One vertical row of screws was 16" from a corner, another row 32" from the first row - surely studs! Nope, I drill through 1/2" of drywall and then another 1/2" of plywood or some other harder material.

What's going on? Is there plywood on the studs with drywall over the plywood? Any clue how I can locate studs with another layer of material in the way?

I can locate studs just fine on interior walls. 2009 construction. No additions or major renovations.