We formulate a general theory of thermal fluctuations within causal
second-order viscous hydrodynamic evolution of matter formed in relativistic
heavy-ion collisions. The fluctuation is treated perturbatively on top of a
boost-invariant longitudinal expansion. Numerical simulation of thermal noise
is performed for a lattice QCD equation of state and for various second-order
dissipative evolution equations. Phenomenological effects of thermal
fluctuations on the two-particle rapidity correlations are studied.Comment: 11 pages, 5 figure