I was wondering if anyone had any experiences with aftermarket cats.....my 98' CLK 320 92k has developed a humming/rattle/vibration and I've narrowed the problem down to my cats. With the cost of a new straight pipe w/ cat at a whopping $1500, I was thinking of going aftermarket. You know, the kind where you have to cut off the old cats and weld the new ones onto your existing oem straight pipe..... Anyone with any personal experiences?