What kind of plane might this have been?

Several weeks ago I was in my backyard, and heard an unusually loud airplane overhead. I looked up and saw it passing by, not as close as the sound indicated, a little larger than the size of my fingernail with outstretched arm. And it looked to be solid gray with no markings. But it was uncharacteristically loud. There was nothing out of the ordinary about its appearance, with one exception: The entire fuselage between the wings and the tail was extremely thin. The wings were perpendicular to the fuselage, and there was just a very thin line connecting the tail. It looked like it wasn’t substantial enough to hold it all together. What kind of plane could this have been?

Powered glider? That would have an outline much like what you describe, and the motors are usually exposed 2-cylinder air-cooled ones and loud as hell.

Yep, I just googled “powered glider,” and some of them look exactly like what I saw.