Trains that 'chug'

Hi all,

First time poster! My son and I have enjoyed starting with TM2, going back to the Tomy trains and now Plarail.

I've noticed some of the trains seem to 'chug' and not run very smoothly. At first I thought this was just an issue with second-hand toys being dirty, but recently I bought one of the ES-08 C12 locomotives brand new with the carriage and it 'chugged' straight out of the box.

Here's a short video of what I mean:



Is this normal? Did I receive a dud? Can it be fixed? Should I return it to Amazon?

Thanks for your thoughts and help