The current European standards demand more energy-efficient, comfortable, and sustainable buildings and encourage the incorporation of recycled materials in building construction. Timber buildings are successfully competing with traditional building materials in addressing these challenges; however, one of the weaknesses of timber systems is their limited sound insulation capacity. One material that can fit into the sustainability aims of timber construction and improve its acoustic performance is recycled ground tyre rubber (GTR), which, on top of this, is a serious environmental problem. This paper presents research on the use of GTR materials combined with timber systems in order to improve their acoustic performance. Three different types of GTR products (granulate, rolls, and sheets) of different thicknesses and densities are selected and are combined with different sound-absorbing materials (mineral wool, cellulose, and wood fibre) inside a lightweight timber sandwich system. In this study, the first qualitative approach, the acoustic performance of the different resulting systems is compared based on the sound pressure level difference measured in a custom-made reduced-size transmission chamber. Secondly, the sound reduction index of four selected specimens is measured in an accredited sound transmission laboratory. The results show that, for all the lightweight timber systems included in this research, introducing a GTR layer improves the acoustic performance of the system.