The single-VANOS unit on S50/S52 engines develops a characteristic rattle on cold start due to failed seals; rebuild kits (e.g., Beisan Systems) restore performance and can produce noticeable torque gains, though many owners report no audible symptoms until disassembly.
VANOS rattle, seal failure, and rebuild
BMW E36 M3 (US-market, 1995-1999) · mechanical