Look at the chain tension on the final drive train section of bike. The smaller chain can be on the loose side. Loosen the rear dive wheel fastners and pull it back to tighten the chain. Mine likes to chain skip and makes a noise at the start of riding or on small inclines where some stress it placed ion the drivetrain. The smaller chain size makes it hard to get fine tuned when compared to regular drivetrain design set-up.

pedaling heard a noise coming from the chain. I wanted to ask them if they know how to fix it. thank you very much!