Impactors are actually a significant hazard to O'Neill cylinders. Unless your megastructure has some well designed mitigation strategies, it's doomed.

That's not an answer to your question, but we have to take it into account in order to answer it.

One of the most practical suggestions for such mitigation is an outer shell that can absorb most impacts, combined with some kind of active countermeasures that can shoot down impactors big enough or with a high enough relative velocity to pose a threat that could potentially penetrate the outer shell.

Most likely, the outer shell wouldn't rotate like the inner shell. There are a number of reasons for this, one of them being it's easier to dock with the thing, another being it's easier to repair the outer shell without having to deal with it having spin gravity that is flinging your repair equipment off into the vacuum of space. There are a number of proposed solutions for traversing from a rotating inner shell to a non-rotating outer shell and back again.

In this case, there's going to be a layer of vacuum in between the outer shell and the inner shell. That means the answer to your question is "totally silent". A meter wide asteroid can crash into your outer shell at 10,000 mph and the inhabitants of your inner shell won't hear a peep. Anyone in or on the outer shell would feel or hear something, depending on a whole set of factors from the material the shell is made of to how far away the impact is to whether or not they're in a space suit.

But let's say you have an O'Neill cylinder without an outer shell (IMHO, if you're going to go through the immense effort to build one of these things, this is a bad idea unless you have some amazing hypothetical deflector shield technology we have no idea how to build) and let's say an impactor gets through your deflector shield. Let's additionally assume that your shell is made out of some kind of meta alloy composed mostly of nickel iron and carbon nanotubes. Something that has the tensile strength to support a 30 km long structure (for the curious, the physics that governs this is exactly the same as the physics that governs suspension bridges). Let's also assume there's around 200 feet of dirt and rock in between the shell and the people walking around on the inside of your space habitat.

The average velocity of a random meteor that might hit the International Space Station is 50 to 100 KM per second. Most micrometeorites that hit the ISS are basically grains of dust and are too small to produce an audible sound. A number of years ago, something slightly bigger hit a window and left some visible damage. IIRC, no one heard it, they just noticed the damage after the fact.

For an asteroid impact to be audible in the environment we've described, it would have to be a significant impactor, big and fast enough to cause significant damage. It's quite possible that the impact could put a hole in the outer shell where dirt starts getting sucked out into the vacuum of space, and the inhabitants still wouldn't hear a damn thing. They might notice a sinkhole forming pretty soon, and that would be no good. (Especially because it means spin gravity is literally helping the vacuum of space to suck material out of the habitat).

If something hits the O'Neill cylinder loud enough for the inhabitants to hear it, in all probability, they have a really big problem.