It is possible that the gearbox is failing or the motor. But both these are replaceable. However, before coming to such a conclusion you may carry out a test. There is a three part component called the coupling spider that transfers the drive from the motor to the gearbox. It also acts as a shock absorber and prevents damage to motorbox and gearbox due to jolts. Hence it is liable to wear and tear as it is made up of plastic parts with a four-pronged part too. Any wear and tear to it results in noise as if there is a mechanical failure. Some of the main reasons that a trolley is noisy is due to faults in the gearbox or faults in the motor. This noise is never accompanied by a motor impediment and hence mostly not given any attention until the noise becomes unbearable. You must understand that this noise indicates the onset of a mechanical failure and hence if possible it needs to be attended to as soon as it is possible.
