Engine knock & rattle: accessory belt pulleys or engine internals?

After replacing the accessory belt and idler/tensioner pulleys, this Ford Duratec HE developed an annoying knock or rattle under certain revs and loads. It's difficult to tell by ear whether a knock is coming from within the engine, or if it's maybe a bad pulley. You can disconnect the belt from the crankshaft and run the engine safely for a short time, to identify if the engine is making the noise without the belt and pulleys being turned. More on the belt & pulleys ~ Replacing the belt & idler/tensioner:    • How to: Change auxiliary belt & pulleys, F...   More on the belt tensioner:    • Auxiliary belt tensioner, noise & aftermar...   Water pump:    • How to (fail): (Nearly) replace water pump...   Over-running alternator pulley (OAP):    • How to: Test & replace overrunning alterna...   Amazon links for the Duratec HE (check your part no.s): Serpentine belts & pulleys ~ US: https://amzn.to/2Gugnmh | UK: https://amzn.to/2GLgt8o 6PK2225 as featured ~ US: https://amzn.to/2TNQpNC | UK: https://amzn.to/2tpyl0v Idler as featured ~ US: https://amzn.to/2BCt0aW | UK: https://amzn.to/2IgAQg6 Tensioner featured (Continental # 49405): https://amzn.to/2VFScG2 More tensioners ~ US: https://amzn.to/2S6gW6R | UK: https://amzn.to/2SFdgy6 Water pump ~ https://amzn.to/2XLTdfC Or, for generic pumps the Ford part # is 1142427 ~ US: https://amzn.to/2ZCqbAS | UK: https://amzn.to/2W5qSAE Alternator over-run pulley, try searching ~ US: https://amzn.to/2lvN0H6 | UK: https://amzn.to/2lvSVfr More detailed links for tools etc are in the specific videos above. Using the above links helps support my channel and is appreciated!