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For a planar FEL configuration we study stimulated coherent spontaneousemission driven by a gradient of the bunch current in the presence of differentlevels of noise in bunches. To perform a vast amount of simulations requiredfor obtaining statistically valid results, we developed a memory and timeefficient one-dimensional simulation code based on the integral solution to aKlein-Gordon equation describing the field evolution. The longitudinalgranularity of the electron bunch density originating from shot noise ismaintained throughout the analysis. Three-dimensional effects like transverseemittance and diffraction are taken into account in simulations via aneffective FEL parameter calculated from Xie's fitting formula. Calculations areperformed for an FEL model with the SwissFEL injector bunch parameters. Itturns out that a reduction of noise by several orders of magnitude below thelevel of shot noise is required to mitigate the noise effect. We propose anovel scheme that allows for formation of electron bunches with a reduced levelof noise and a high gradient of the current at the bunch tail to enhancecoherent spontaneous emission. The presented scheme uses effects of noisereduction and controlled microbunching instability and consists of a laserheater, a shot noise suppression section as well as a bunch compressor. Thenoise factor and microbunching gain with and without laser heater areestimated. We found that shot noise reduction by three orders of magnitude canbe achieved for a finite transverse size electron bunch.

Stimulated coherent spontaneous emission in an FEL with `quiet' bunches