Rain noise in gutter downspouts appears to be very common problem all over the world. People cannot sleep, cannot work, cannot focus on something while it's raining and there is downspout nearby. The dripping rain sound in downspouts is very annoying noise that may drive human mind crazy even on unconscious level. Most people having problems with rain noise when trying to fall asleep or they wake up in the middle of the night due to that noise.
It appears to be common problem in first floor offices also. Employees tend to be less focused on task at hand when it's raining and there is downspout near the window. If you have to work from home or run business at home you probably noticed that rain noise in downspout distracts your attention from whatever you attempt to accomplish during a rainy day.
There is simple and effective solution for this common problem. Downspout Insert rain silencer is product specially designed to fit most downspouts and eliminate rain dripping noise in gutter downspouts completely. It's made from material that quiets falling rain drops, never absorbs water and drys up fast. Most of other material people use for that purpose will mold and disintegrate under influence of water and sun but not Downspout Insert. This insert will stay in place and serve its purpose for years. And did I mentioned that anyone can install it in seconds? Literally, you open a box, place insert into downspout and fix it with stainless metal clip provided.

Many people say that they are not willing to pay $10  to resolve a problem they can figure out how to resolve themselves. Fair enough... But think for a second how much time you put into it... At least 30 min to do some research online, then searching for the right material that may turn out to be not the right one after all. Or you need to drive to a store to get the material, to cut it right and fix it so it stays in downspout. All that can easily turn out to be hours and cost you some money also... 
So why bother "reinventing the wheel"? Just get "ready to go out of the box" solution and forget about rain in your downspout for long time.

Good luck!