Very few of the tubs are true to round. You stated it has made the sound since you've owned it. Observe and listen to see if you can determine the closet area to the noise. Usually moveable parts get louder over time. Your problem could be a number of things. I would start by adjusting the bottom leveling feet and be sure it is level front to back as well as left to right. Other items could be drum seal gasket bearing, rear felt seal, rear drum support roller, belt tension pulley, blower wheel, blower wheel housing, front drum glide bearing, shaft drum support roller, bracket for drum support roller, front ring bearing kit, pully on the motor, or even lose cabinet housing bolts.
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