I would agree with everyone get the motor rebuilt or change it out.
I had a tick in my 2000 4.3 170,000 miles and tried motor flush and different viscosities of oil.
Within a week the ticking became knocking and when I got the engine rebuilt it cost a little more than a standard long block because I smoked the camshaft.

 

Update:

Just found out the dipstick in the motor is the wrong one for my blazer. The oil level on the dipstick indicated overfull oil, but we didn't put very much in it after putting the oil pan back on.

Could it be just a bad lifter?

Would it really be a bad motor if the knock comes and goes?

or just really really low oil?

what about oil pressure lines?

 

so what was the problem?mine was fine.(2000 2door 2wd blazer LS model)got Tboned by a 92 yr old goin 65+ in a 35mph zone right into the driver door.worked my magic and had it bk on the road in 6 days(me and my moms only ride)both motor mounts and tranny mount were snapped and engine was sitting on the pass side of the engine bay with a 25 to 35 degree tilt and my dumb brother drove it home at 10- as fast as he could handle speed,EVEN After i told him to tow it home.
Well a month later i started it and it had a tickticktick noise,still does,but once it gets warmed up to aropund 130-170 degrees it goes away,but every blue moon it ticks realy loud and doesnt want to stop or go away,so at those times,I turn it off,And restart it within 10 seconds,and then it starts with the tick/knock-But goes away like it does on normal regular tick start ups,the tick fades away like its finnaly getting oil to it.so i figure its a valve or lifter sticking or clogged from the impact.bought i new head from autozone but havenmt tore it apart yet?
SO I`M WANTING TO KNOW IF I`M ON THE RIGHT TRACK?OIL P.S.I. NEVER LOWER THEN 40-45,AND THATS ONLY EVER BLUE MOON.ANY HELP THANXS N ADVANCE N GOD BLESS,CHARLIE.

 

I think we need to differentiate between a tick, tock, knock and bang. Tick is generally lifters or clicking injectors. Tock is excessive valve train clearance or a lower end bearing getting ready to go. Knock is rod or main bearings are gone. Bang is self explainitory.