Two things bug me in particular. Rust eschews readability by erring on the side of terseness — fn instead of something like func, for example, might save some typing, but does contribute to making visually denser.
The choice of snake_case instead of camelCase also adds to the noisiness, because there's no programmer font that aligns the underscore with the text baseline, so it's disruptive. Snake case is pretty aptly named; typographically, there's a lot more visual cohesiveness to camelcase. (As an aside, I never understood the lack of consistency here: the capitalized version of foo_bar should surely be Foo_Bar, not FooBar.) Python admittedly uses snakecase, but avoids looking too ramshackle by having otherwise very little noise.
Compare something in Rust (from OP's repo):
fn type_list<'a>(dex: &'a DexFile<'a>,
off: u32, parse_cls_desc: bool) -> Vec<&'a bstr> {
func typeList(dex *DexFile,
off uint32, parseClassDesc bool) []BStr {
Of course, Go doesn't have lifetime annotations, but I can't understand who thought using ' was a great idea.
I wish more time was spent on the visual aspect of a language. I'm really liking Reason, Facebook's new syntax for OCaml, which shows that a language can be made fresh and friendlier through aesthetics alone. Elixir is cleaner than Erlang, but I think it went too far in emulating Ruby; instead of very simply aligning "def" and "end", for example, you now have "do ... end" everywhere).
Edit: Typo.