We demonstrate frequency differential CARS (D-CARS) using femtosecond laser pulses linearly chirped by glass elements of high group-velocity dispersion. By replicating the Pump-Stokes pair into a pulse train at twice the laser repetition rate, and controlling the instantaneous frequency difference by glass dispersion, we adjust the Raman frequency probed by each pair in an intrinsically stable way. The resulting CARS intensities are detected simultaneously by a single photomultiplier as sum and difference using lock-in detection. We demonstrate imaging of living cells with strongly suppressed non-resonant background. We also show D-CARS using a single femtosecond laser source.