i'm assuming yours it 2wd?, if it is, piston slap is common from cold, mine suffers from it but goes away after a few mins

piston slap is mainly caused by the con rods being connected dead centre to the pistons. 4x4 engines done suffer from piston slap as the con rods were connected to the pistons off centre.

i wouldnt worry, i believe even the 2wd ford manuals advised of piston slap (although probably worded differently)