Not possible to tell without a picture, and probably not even then.
I've had ferrous metal settling out on my dipstick (though it was typically left longer than overnight). Best guess is it came from the cams
I believe it was ferrous metal because it looked like it, and because a magnetic pickup tool left in the dipstick hole seemed to collect quite a lot.
Last edited by Ducked; 02/09/18 01:53 AM.