Forgot to mention something. I didn't realize there was a cavity at the front of the motor that gave access to the underside of the intake manifold. A rodent must have gotten in there to store some reserves for the winter. See photo. I snaked an inspection camera in there and discovered them. They could have been rattling against the knock sensors leading to unneeded timing adjustments by the PCM. I tied a small flexible hose to the camera arm, then to my shop vac, and surgically removed them. I should have gone to med school.
