Engine knocking suburban

Recently my suburban has started to make and
engine knock. I know most of the possibilities that
cause this but the strange thing is that sometimes it
does it and sometimes it stop. Sometimes it will
even do it in the morning after a cold start. Recent
things that have happened to the car were replaced
spark plugs, catalytic converters, and a recent front
end crash that caused the replacement of the front
bumper, lights, hood, and grill