I've had one record affected such as this, with a very clear rectangular pattern. For me the culprit was easy to identify. My Pink Floyd "The Wall" double album has a rectangular fogging on the A side of the first disc, the face that would be closest to the front of the gatefold. As you probably know that gatefold came with a vinyl cling "sticker" on the gloss surface of the album. It wasn't really a sticker since it didn't stay attached with adhesive. It was a similar material to a car windscreen badge. So, the original "Pink Floyd "The Wall"" Logo wrecked the LP as it sat in storage for a few years in the attic. The fogging is the exact shape of the sticker and in the exact location I had that sticker on the album cover. Watch out for this one, and watch out for whatever other albums you leave resting against "The Wall" in storage.