My 2001 Suburban has recently developed a loud rumble in the rear when going over rough road or bumps. Years back I'd gotten a noise at higher speeds on the highway but that turned out to be a loose heat shield on the muffler which I had fixed. I did drop, clean, and lubricate the spare wheel lift cable last fall, but I checked that and it appears to be snug up against the frame as it should be. Rear stabilizer links have been changed not that long ago also. Any ideas?