That's one vote for amplifier and one against actuator. For $50 you certainly became an expert! I'm inclined to buy the cheapest WORKING amplifer I can find and try and figure out how to put it in.

My 350 is as smooth as can be--the hood doesn't jiggle at all but you can definitely hear it. It reminds me of my former BMW 524td, but it is way, way more powerful. I like the distinctive sound. One thing I do is keep a container of fuel additive in the trunk and add it most of the time; I buy it at truck stops for about $15 a gallon. And I keep a small glass jar with it to pour it because it eats right through cups. I did the same thing, plus trying many other brands, with my previous Mercedes diesel and it didn't really do anything--the car was always rough at idle but smooth at higher speeds. I thought it needed new injectors.

I'd certainly like to hear of any flaws with this engine.