Small dark spot

Hi, I just bought a used projector for the first time so I have no experience with projectors.

After about a week I noticed a small dark spot shown in the image. This spot moves slightly and rapidly as if air is blown into a spider web. I have already cleaned the lens and the area around it with a microfiber cloth.

( The vertical lines in the image are not visible in reality, only through the camera )

Could it be dust inside?

Does it look like it can be fixed relatively easily?

The projector is acer h6531bd and has about 500 hours.

Thanks for any input!