Problems with our underwater treadmill

[Guest guest]

Our treadmill a Heido, from Germany, (purchased before I started doing rehab)

and is about 5-6 years old. The main pulley belt keeps " knocking " and/or jumping

the gears. We had some pool guys working on it at first with success for a few

weeks or months and then the " knocking " would return. The past two to three

weeks we have had a man that works for a welding company on conveyor belts

working on it. We have replaced almost every part imaginable and the " knocking "

continues. Has anyone else had this problem or have any suggestions on how to

fix it.