Open
the
timing
chain
cover
and
inspect.
A worn nylon top gear on the cam will create slack in the chain that causes it to pile up on the opposite side resulting in a sound exactly like this. The bottom gear is steel so it maintains pull on one side while tension is slack on the other side due to the worn top gear.
It will also explain the delay in the sound appearing after start up as it takes a second or two for the chain to pile up once running. The piled up chain may also rub on other parts to make more sound.
It’s a simple thing to check, it’s your choice whether or not to do it.
