Just a thought - a "marbles rattling in a can" sound is often pinging. If you have an air leak of any sort, the car would run lean, then run warmer, and then would ping due to the extra heat. Jeff Aronson Vinalhaven, ME www.landroverwrter.com '66 Corvair Monza Coupe 110/4 '66 Land Rover Series II-A 88" [2] '80 Triumph TR-7 Spider