If it has a low pitch growling when you start unit then the running belt is too tight and the adjusting bolts need to be backed until the growling noise is lessened or eliminate without the running belt slipping. If it is the drive belt slipping, the adjustment bolt is underneath the frame so you will need to elevate the treadmill and adjust the bolt until slippage is eliminated without over tightening the drive belt.
Answers & Comments
If it has a low pitch growling when you start unit then the running belt is too tight and the adjusting bolts need to be backed until the growling noise is lessened or eliminate without the running belt slipping.
If it is the drive belt slipping, the adjustment bolt is underneath the frame so you will need to elevate the treadmill and adjust the bolt until slippage is eliminated without over tightening the drive belt.