An emission from relativistic electrons crossing an aligned crystal is considered with account of coherent bremsstrahlung on atomic strings and transition radiation contributions. Some peculiarities in the low energy range of the emission spectrum caused by azimuthal scattering of emitting electrons on atomic strings and an interference between the transition radiation and coherent bremsstrahlung are predicted and analyzed theoretically. (C) 2004 Elsevier B.V. All rights reserved.