Sump replacement engine noise

The sump on a K10 had corroded. Apart from that the engine was fine and ran sweetly. I fitted a new sump and now have a clattering sound. The only thing I had done when the sump was off was to remove the oil strainer to clean it. I have checked valve clearances. Any ideas?
 
Thanks for the comments. Nothing loose in the sump. The new sump was very slightly different from the old with an internal baffle just making contact with the engine block, it must have set up a resonance. A few minutes with a file making sure that no swarf entered the sump and it was refitted. As quiet as ever it was now.
 
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