Pinging or Rattling Noise

Dear Bob and Ken, I'm based in Taiwan and my car is a 2006 Model Mercedes Benz W211, E 280 (3000c.C.) V6 GAS, Done only 9300 Kms, Automatic Trans. Lately, I noticed after driving for about 15 mins. After start. I hear a rattling noise from the engine everytime I accelerate even if I was driving alone without any load and in almost any shift, first to fourth or fifth gear I guess. And also a VERY VERY slight knocking noise like a diesel engine on idle. I had it a complete computer check and a tune-up. The Knocking Sensors are ok, the spark plugs are very clean, the air filter is replaced. But still didn't eliminate the noise. I use 95 & 98 octane which I believe is only an equivalent of 91 & 93 octane in the US. The knocking noise is much often and obvious when I use 95 octane. But, although the noise is lot lesser when I use 98 octane, somehow its not 100% gone. Power is ok both with 95 or 98, just slightly more powerful with 98. I've read a lot of your answers about the EGR valve and I'm planning to have it changed as probably it wasn't detected by the computer analysis. With respect, my question is what else could I do if after replacing the EGR and still has the noise? I only have 9300kms on it and its almost new. Does this normally happen on a very low mileage car or could it be a factory defect? Your answers will be highly appreciated. Thank you and All the best. Jessy S