Rod knocks are usually much deeper sounding, and more consistent. They usually knock loudest under part throttle loads... but usually in a more consistent manner.

Yours on the other hand, sounds a LOT like mine did. Mine started as more of a tick that would come and go. At first I wasn't even sure it was coming from the engine.

Before I go further however... this kind of tick can also come from a cracked flexplate.. which is fairly common. Hopefully that's all it is. If it is a cracked flexplate, it can be changed without fully pulling the transmission. But you would have to move the trans back far enough to get to the flexplate bolts. To determine... I would recommend disconnecting the torque converter (3 bolts) and push it back, away from the engine. Try to see if you can visually see a crack around the crank bolts. Run the engine (with torque converter disconnected) and see if it still ticks. If it doesn't, you've narrowed it down to (most likely) a cracked flexplate, or otherwise transmission trouble.

Mine still ticked. This tick went on for weeks, slowly got louder and more steady. Eventually the tick became more like a knock... louder and more steady.

I finally pulled my oil pan for inspection, and immediately found a piece of broken piston skirt down in the pan. Next I noticed a burnt wrist pin at the same piston. THE END.

I was happy to have gotten 282K miles out of my faithful 4.3.
I replaced it with a V8.

Cant say your situation is the same as mine... just sharing my story.

Also, be sure to disconnect your serpentine belt to rule out any turning parts that could have issue and make a noise.

Good luck

 

hi
i have that problem with my trail blazer
it don.t knock all the time and sound
doe's not change at different R.P.M.
me and my circle of people can not figure it out

oh by the way 4.2 motor
265854 miles

 

I had a Caprice that cracked a flexplate, it too had intermittent metallic noise. An oil pressure gauge might help diagnose the noise if it turns out to be bearing related. A long stethoscope could help as well.

 

Thanks, I appreciate the input. I'm going to crawl under there and start poking around. The sound is loudest underneath the motor--sounds like playing cards in bicycle spokes.

 

I got a replacement engine for Randy's '93 Astro ( :lol: ) cheap because the kid pulled it (after doing a crap ton of top-end work) for an engine knock...that turned out to be a cracked flexplate. Someone had given him a 350 for free, so he popped that into his Blazer instead.

It's a common problem on the 4.3.