Hi, I am noticing the same problem. Bought a 2nd hand C5 tourer 2011 (2.0 HDI, 163 HP, exclusive, automatic) with 130k km. Loud knock (actually a BANG) occurs on both sides in the front when I drive over a speed bump. The exact movement that causes the knock is acctually front suspenssion extension move. It doesn't knock on compression or small bumps, only on a fast extension move. It seems that a certain threshold of "extension speed" has to be reached for knock to occur. From there on, regardless of the speed, loudness is the same. Otherwise, susspension works perfectly. To bad I can't take advantage of superb floating ability over speed bumps as it becomes so loud. Anyone solved the problem?
