my car started knocking as soon as the temperature dropped into the low 50's.

Check your oil level.

Owner: Possible causes for engine noise of this type: Neglected maintenance,ie:low engine oil level, incorrect viscosity oil, overheat damage,worn / loose timing chain or faulty tensioner /guides,sludge contamination, restricted oil pump screen, also: cracked flywheel, loose flywheel to torque convertor bolts, faulty serpentine belt(s), serpentine belt tensioner, or accessory bearing issue.