Please read the instruction manual. Some treadmills need periodic belt lubrication and adjustment. They will just work better if you can plan for this.
For heaven's sake, don't throw it away!. The part probably worked loose and dropped. If you are not sure where it came from, keep it in a parts box and let me know when I drop by to put it back together.
They wear out! Plan for having replacements in stock and ready to use.
Funny enough, these can short circuit as well. Firstly, don't wind them up really tightly around anything. A loose wind will prevent the internal wiring from breaking due to repeated bending. Also, it's a good idea to have an extra set of leads ready to use should one set stop working.
Given that the head is producing a high frequency transverse wave, the ultrasound eventually shakes itself apart. It is not likely that you will see parts falling off the head, however it will eventually be producing no effective ultrasound wave. This is why I come by to certify effective operation.
Shockwave tips need to be rinsed off after EVERY use. If you use gel to lubricate the skin surface, it will gum up the tip when it dries up and the tip becomes ineffective.
Also, if you have a water trap for the unit, it needs to be checked weekly and emptied as needed.