Ensemble rehearsal is inherently collaborative and performance-oriented, but these characteristics do not necessarily make rehearsal project-based. This article examines how project-based learning (PBL) can be operationalized within short, performance-linked co-curricular ensemble rehearsal in higher music education. It presents a practice-led analysis of the pedagogical design of Ensemble Groove Labs developed within a contemporary vocal and instrumental ensemble at a Singapore university. Rather than evaluating student outcomes, the analysis examines how established PBL principles were translated into rehearsal structures under the practical constraints of limited contact time, mixed musical backgrounds, and an existing performance calendar. The design combines an explicit musical inquiry problem, recurrent rehearsal loops, distributed student leadership, lightweight planning artifacts, critique and revision, reflection, and audience-facing performance. The analysis highlights a distinction between rehearsal that is merely active or collaborative and rehearsal deliberately structured around project-based inquiry. It further shows how lightweight scaffolds can externalize musical decisions sufficiently to support collaborative testing and revision without converting co-curricular rehearsal into a paperwork-intensive academic module. The article offers a bounded design account rather than evidence of causal learning effects or a validated intervention. It contributes a rehearsal-specific approach to adapting established PBL principles to the temporal, organizational, and artistic constraints of co-curricular higher music education.