Knock in my engine? or pulley noise??need help. Car:2004 Mustang gt miles:115k miles?

My car has had a knock noise from the day i bought it should have been a red flag but i test drove it and it drove fine. Recently did an oil change and my timing chain guide broke and clogged up my oil screen so i had new timing chains guides and chains along with new tensioner and water pump as well as new seals and gaskets replaced at my mechanics shop when i heard it start again the engine bay was a lot quieter than before but the noise has come back my mechanic told me he found no metal shavings in my oil pan and that my cams and valves looked fine, the noise is present at cold start and warm up but can be heard clearer when i have it in drive or reverse. transmission shifts fine also. any suggestions on what it could be? i also changed the spark plugs with ford oem plugs about a month ago i havent changed the coils though. car starts up just fine oil pressure is now back to normal after having timing chain guides removed from oil pan. drives good a low speeds and highwayspeeds.