So here's a strange one. 1999 Suburban C1500. 230k miles. Recently the truck developed a vibration starting about 45 mph. Kind of a moaning sound that got louder and more easily felt as speed increased. Feels like it's the front to me. Front tires were getting old so I had them replaced, vibration went away for about a month. Yesterday I hit a MILD bump in the road at 45mph (definitely not a hard hit) and the vibration instantly came back. Oddly the vibration almost totally goes away when I'm braking. Not totally, but very noticeably. Front has all new Moog ball joints, tie rod ends. Brake pads have maybe 12k miles on them. U-joints on the drive shaft have no play (i have not removed the shaft, just tried to jiggle it in place, it's solid in that regard). Front wheel bearings are about 5yrs old, repacked about 2 yrs ago. I haven't had a chance to jack it up since yesterday to inspect. Any suggestions?