2K2SilverTL-S

The other day I noticed that around ~3500 RPM's there is a slight rattle from the engine bay that goes away once I hit ~4000 RPMs. I don't really here the noice under full throttle because the RPM's fly up so quickly, but under light to medium throttle application, the slight rattle is evident everytime at around 3500 RPM's. I dont think the actuator is broken because VTEC still engages and that sonorous roar and pull at the higher RPM's is still there. Have you guys noticed anything similar or heard of anything similar to this?