Portable generators.

[Irving]

Would it be safe to put something like this in an insulated box? Run the exhaust through a muffler? I'm just interested in keeping sound to a minimum.

Excellent question. You might run into cooling issues if your box is too insulated. Seems like a muffler exhausted outside, and the generator inside a garage would be pretty quiet. <-- I only say that because my neighbor has some family living in an old RV in his driveway, and I occasionally hear them crank up a generator. The generator sounds as old as the RV looks, and I would never hear it from inside my house.