This page explains the rhythmic thumping or sometimes referred to as the “heartbeat” noise a treadmill makes when the running belt is moving. This is a very common question especially for new treadmills or replacement running belts.
What causes the sound?
The noise is a result of the treadmill running belt joint going over the rollers. As the joint is marginally thicker (two layers) than the rest of the belt it induces a slight pressure wave when going over the rollers. This can commonly be described as a rhythmic thump noise or heartbeat and will increase in frequency as the belt speed increases. This is totally normal for all treadmills and especially so for a new treadmill. The belt will become more supple over time which will reduce the noise but keep in mind that the joint will also be there.
Do NOT tighten the belt to reduce the noise, it will prematurely wear out the motor, roller bearings and running belt.