I got a TMJ arthroscopy done 8 months ago. I have a feelingthat something is there and I hear cracks. What could be thereason of still getting inflammation?

No surgery 100% Arthroscopic surgery has a success rate somewhere between 80-90%. If your symptoms are still unacceptable, you may need another scope, arthrocentesis, a steroid injection, or open TMJ surgery.
New problem. Probably from continued joint degeneration. If cause of TMJ symptoms was not treated, most often that means correcting malocclusion (see an orthodontist) joint will continue to deteriorate. Go back to surgeon for reexamination.
Joint swelling. Could be more adhesions forming (scars) or disc perforation. You might want to take another mri.