INTRONS HOUSE MOBILE ELEMENTS. “About 40% of the human genome is comprised of intronic regions; however, this figure is likely an overestimate as it includes all annotated events. It is also important to note that a large fraction of TEs and repetitive elements are found in introns.” (TE = transposable elements).
http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1004351