Help...what causes this big brown patch?

I have a mystery on my hands and I'm looking to this forum for help. My otherwise beautiful lawn ALWAYS develops a big, ugly, rectangular brown patch in the same spot, year after year. I'm almost positive it's not grubs...I've had those in other areas, and the grass doesn't pull up like it does with grubs. Just gets really brown and ugly. Last year I dug the area out, put in new soil and seed, and this year it still happened! What's going on? Tried to add an image below...