The EF 70-200mm f/4 is quite a quiet piece of lens. The sound you described should be normal.
No longer are these new lenses as noisy as the older EF lenses when they do AF hunting, when you can actually hear some 'banging' sounds.
Do a comparison with another 70-200mm f/4 from the shop that you bought, and you will have a rough idea.
... unless yours is particularly noisy, then may need some CSC help.