hmmmmm...clanking sound. It sounds to me like there's some wear ocuring in the of the motor either in the cylinders or in the bottom end bearings. The sound may be happening when it's really cold and the the tolerances between bearings or cylinder rings are opened up until oil gets in there and some heat builds to close them up. Keep a close eye on your oil usage, if it gets higher than 1 quart every 1000 miles, it's time to start looking into some engine work. Get a compression test done, those results will shed more light on the issue. If the test reveals that you aren't holding good compression then it may be time to start looking into engine work sooner rather than later.