Engine knocking

[TjXiong]

My engine have been knocking from my first oil change
i had the car with 25000 miles on it
i took it to a performance shop
and they say that it might be a lifter
one other dude says the same thing
i was thinking about a rod
the knock comes when the engine is cold and once you start it up it knocks
once the engine is warm and being driven for 30 min it stops
but once in a while it comes back again (a on and off thing)
i try changing oil using different one.
need help
(420a motor)