Check the obvious things, fluid level, replace filter, belts for tension and you might even want to bleed it as air can cause noise...then when you are done with all of that and accept it then you can say at least you tried. My 280 made noises like that the whole time I owned it...I just learned to live with it after wasting a couple of hours trying to fix it.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz