Block and Weinberger show that an arithmetic manifold can be endowed with a positive scalar curvature metric if and only if its $\rationals$-rank exceeds $2$. We show in this article that these metrics are never in the same coarse class as the natural metric inherited from the base Lie group. Furthering the coarse $C^\ast$-algebraic methods of Roe, we find a nonzero Dirac obstruction in the $K$-theory of a particular operator algebra which encodes information about the quasi-isometry type of the manifold as well as its local geometry.