If it sounds different than normal operation, it does not necessarily mean a malfunction, but might need to investigate further. Trace the source of the noise. Look back what the operator did differently before it started to happen. Look for signs of internal wear.
However, if you don't have a lot of experience with the machine, be more cautious. Depending on your industry, lots of machines can sound like they're going to fall apart any second when they're running perfectly fine in reality!