Many car manufacturers are introducing Stop & Start systems based on conventional ring gear starter, which represents an economical solution without heavy modifications of their existent architectures especially if they consider hybrid technology. However, this solution is unfortunately not very satisfying from NVH point of view. Indeed, customers usually accept a noisy and quite long engine restart when it happens only one time at the kick-off. However, for hybrid vehicles, an inaudible and quick restart is required because it happens without any drivers' demand and thus it may disturb them.In this paper, we focused on NVH analysis of engine restart sequence with conventional ring gear starter. Some solutions were tested in order to optimize restart duration and noise level. Permanently engaged starter and high power starter are two simple and economical solutions that allow reducing significantly both starter noise level and engine restart duration, which makes this technology acceptable for hybrid vehicles.