Symptoms

You may hear a clapping or slapping noise coming from the treadmill running belt while running.

Cause

The most likely cause of this noise is that the running belt is overtightened. This frequently occurs if the belt is manually tightened after the first few uses.

Why does it happen?

If the belt is too tight, it loses its natural sag and floats tightly above the running deck. Because the rollers sit slightly higher than the deck, the belt is suspended. Each footstrike forces the belt down, causing it to hit the deck and create a slapping or clapping sound. This is usually more noticeable near the front roller, as most people tend to run closer to the front of the treadmill.

How to check

You can often identify an overtightened belt by checking the rollers. A belt that is too tight will quickly leave an imprint of the belt on the roller.

Solution

To resolve this issue, the running belt tension must be reduced to the correct level. 

How to adjust a treadmill belt