For sure the quality gap is closer than it once was.
Rattles can happen for any number of reasons, in my BMW the rear parcel shelf knocks over bumps and makes an annoying noise. The interior isn't falling apart though.
Also, you tend to find the painted silver plastic metal effect trim consoles in Fords, Vauxhalls, Renaults etc.. is actually real metal in German cars. The leather on the steering wheel doesn't melt as it does on all Fords I've driven.
These are trim rattles and some of the fit and finish are questionable, doesn't make a very good impression when you have high flying clients being driven around. Also the metal are not real on every German cars, the so called best interior maker Audi use swathes of painted fake alu trim. But in general yes a Merc will be better in that respect over a Renault as you would expect, but that still don't justify the huge premium, you can't just rest on the laurels of perceived better interior materials, there is more to a car.