Each generator will have different layout on mounting so some study of what you have will be needed but I've just gone through building a "shed" for a portable here at home and there are some common ideas that can be used when dealing with sound.
Step one of course is to not make as much to start but that's not an option with a noisy one like you have.
Step two is learning how sound travels and that leads to what you can do next.
What I found was deflect first as the sound waves tend to move in straight lines that can hit slanted walls to deflect them down or away from where you want quiet. Deflecting it down so that it hit soft dirt is good!
But then you will also want something to "soften" or break up what is still a problem, so layers of differing materials is a good next step. I found panels made of cardboard, forming a "sandwich" of other layers of a fabric packing material and then foam insulation board cut my noise way down.
Doing this on a built-in generator is going to be much harder due to limits on space but playing with the different methods may get you closer to what you want. Simply wrapping the genset in any material is not going to work due to the heating factors. Directing the exhaust up will get some but much of the noise comes directly from the generator body.
One handy tool to use is to download a sound meter for your phone as it gives a much more definite answer than our ears which are pretty unreliable.
One first thought might be to look at hanging something heavy like packing blankets, stapled to something firm like cardboard at an angle to slant the sound down to the ground. At least this might be done on the outer edges, where the noise is most prone to be a problem.
Not an easy problem to solve but it can be made better.
For details on what worked for my specific want/needs, this is the posting but it got way too muddy at the start so you might want to skip down to post 29 to get into anything usable!