I have Crohn's only in the terminal ileum, but I also have cramping in the large bowel occasionally. Often if I sense a cramp on the left-hand side or lower abdomen, and touch that spot, and I can feel either gas or a BM in the colon. I developed this after I was hospitalized, took a lot of antibiotics, and went about
four days eating only sporadically.
I explained my symptoms to a gastro and was told I have spastic colon, a.k.a. IBS. Since I only have Crohn's in the TI, I pretty much write off cramping anywhere else as IBS (I do "palpate" to check for real pain, never felt it though). I don't think it's uncommon to have IBD and IBS in the same person. My GP told me that using a soluble fiber supplement could reduce colon spasms.