'15 Prius C Experiencing 'Prius Death Rattle'

Did the intake manifold get cleaned too? It’s the last leg of the Exhaust Gas Recirculation circuit, has a large intake gallery, and four capillary passages, one at each port. Pay special attention to the latter. Brake cleaner and brushes/rags will do the trick. A skinny pipe cleaner type brush is good for the capillaries.