Loose Rocker Arm

[CB1987]

I've been hearing a tapping in my engine at certain RPMs since my 350 had a full rebuild from acertified mechanic . Brought it to him and he said it was just something loose but not involving the engine. After checking every nut and bolt I did some research. Came up with the valves needing to be adjusted. I popped off the valve cover to see if it is something I could do. Going through and wiggling the rocker arms, about 50% of them were able to move with little force. Since I have a warranty I figured I would leave it to my mechanic. Sorry for the long breakdown but they should all be equally tight regardless of the position of the pistons right? Thanks for the help!