When you say "rust," do you really mean a maroon, burgundy, deep red sort of color? With the inclusion of air bubbles, this sounds most like cyanobacteria. You should be able to siphon it off in big sheets. It's a fairly normal part of tank cycling, and will almost always go away on its own, but it's annoying as heck in the meantime. I siphon it off when I can.
The only truly "rust-colored" entity I can think of is red planaria, which are individual flatworms (sort of squarish). They can multiply and often look like sheets, but do move individually.
Google pics of cyano - that's what I'd bet you have.