420A 420a knocking?

[2gev]

The other day i noticed my 420a began to develop a knock or clang, seems to fade as i rev the car but is quite loud at idle and when i rev the car and it returns to idle its loud from about 1500-idle and then at idle its quite audible, pulled the pan down just to see if there metal or bearing material in the pan, pan is clean enough to eat on, oil pressure is 65 cold, 25 warm , 65-70 cruising speed. stethoscoped the motor sounds to be coming from cyl 4 bottom end of the block, do i go thru and attempt to replace the rod bearings as i can do that with the motor in the car still, i had just put this motor in maybe 5 months ago and i dont beat on the car just work and back, just finished my manual swap and put 300 miles on it for this to begin to happen, any advice would be great, ive pulled this motor maybe 4 times over the years and just really do not feel like doing it again if i dont have too, any common issues i should be looking for? Valve lash, wrist pin etc, thanks guys

 

[2gev]

motors got 124k on it

 

[2gev]

another note sometimes it’s almost completely inaudible and other times it’s loud , usually when reving it lightly to about 1300 it comes back and then fades out