Is the noise getting louder had the same problem with my 02 xterra S/C it had 50,000 miles when the supercharger went out. Have you notice that your X lost power if so that's the problem S/C. Good luck hopefully it is not the S/C cause it cost me 5,000 to replace. Look around your area try to swap in a Titan v8 could be around the same price range seen some xterra's with v8's cray fast