Streetrod19772000

I have a 96 tacoma with a clattering noise. No noise on start up probably because of higher idle speed. At 1 minute you start to hear a lite clattering sound that increases in sound for 5 to 7 minutes. After truck is up to temp sound goes away. Now after another 10000 miles can hear light clatter even after warm up. I have replaced exhaust manifold and cat because manifold cracked and cat had an internal rattle. Is this piston slap? Balance shaft? Valve lash is good. Does anyone know what this is or has anyone tore down their engine looking for cause of noise??