Manufacturing DVDs is similar to stamping coins; metal stampers mold polycarbonate plastic substrate. DVDs have a wobbled spiral track (not unlike vinyl records) pressed into the plastic by the stamper. If the stamper is not perfect (and none of them are, really) you get some groove imperfections, a fraction of a micron in size, that interfere with data synchronization along the groove during recording. That occasionally results in a few thousand erroneous bytes here and there, and is corrected during reading by the error-correcting code. One stamper is used for tens of thousands of discs, so you see the same microscopic defect repeated in all discs you get in one spindle, resulting in the persistent spike that you noticed.
I didn't mean to say that the discs are defective in any way. They are not pushing the error-correcting code anywhere near its limits.