CD,
What I had been reading for years about defragmenting drives is that you don't do it for your DAW's audio drive(s). Supposedly defragmenting is supposed to help the drive read single files, but with multitrack recording, the drive is jumping all over the place to read multiple tracks. And defragging can make it worse by potentially moving tracks in the same project further apart.
But it did work for you so it makes me wonder.
Mark