I have recently bought a 2013 SLK250CDi which I really enjoy. The only thing I find is the engine is sooo noisy; I also have E350CDi which is in a different league refinement wise; however it's great fun to drive and really nippy; it's just very unrefined; when it is idling after warm-up the revs seem to sit at same place as when cold rather than drop back like my 350CDi? Anyone else have same experience?