SLK 200 172 1.8 turbo engine note

[blitzracing]

I've recently acquired a low milage 2016 SLK 200 172 with the 1.8 turbo motor. It has a slight warble to the inline 4 cylinder engine between about 1200 and 2000 RPM, a bit like a flat 4 boxer type engine but it sounds pretty normal above 2000 RPM. Otherwise the idle is rock solid and engine smooth. There appears nothing specifically wrong with power output or with a full OBD diagnostic, but I've never heard an inline 4 pot like this before, and I'm not familiar with this specific engine note. Does this sound normal for one of these Merc' engines before I start pulling plugs etc?