Actually, I don't see a cover, and I have no idea what kind of noise you're hearing. You didn't bother to list the engine size or mileage so I can't make any generalizations to problems that occur based on mileage. The only thing I can guess is there was some type of plastic cover on the center bolt for the strut. If that is correct, that is there to dress it up under the hood. It has no mechanical function other than possibly deadening a little road noise, and it won't cause any real noise if it's there or not. Most cars don't have a cover there. Missing it is not a safety concern. If you want to replace it, you can find them in salvage yards. This type of thing has very little demand so the cost will be pretty low.
A noise over a bump is often caused by a worn strut, worn upper strut mount, anti-sway bar link or bushing, or even loose brake pads. None of those things have a big effect on safety. There could also be a worn ball joint or tie rod end. Those can be a safety concern. The people at tire and alignment shops are experts at finding the causes of noises, vibrations, and bad tire wear. Have them inspect the steering and suspension systems.
Thursday, October 29th, 2015 AT 7:50 PM