Let me begin by saying I am new to the forum and this is my first post, I will try to follow all the rules for posting that being said if I do break a rule I do apologize. Let me know and it will be corrected! Now it’s time to get down to business.
I have 99 Camaro with the 3800 series 2 3.8L with the hydra-matic 4L60-E electronic 4speed with the lock up torque converter that locks in high gear, fancy way of saying “stock” so the other day we was stopped at a red light when we went to take off it acted real sluggish (after initial take off) my wife said it done it once before a week or so before ( it’s her everyday driver) she said when it did it before she pushed the gas and it felt like it blew something out and it was good after that! (I was as surprised as you are when I heard it too) So we get the car home and begins the troubleshooting process) there was a knocking sound that developed not a rod or bearing knock more like a rubbing kinda knock at first I though it was a flywheel bolt or torque converter bolt that came loose check all the bolts they where good, the car cranks good but knocking (at idol and when accelerate it gets faster with rpm)
i am gonna run the overhead on it today but I was wondering if anyone has had a similar problem before? I am very mechanic knowledgeable just haven’t worked on a lot of automotive, I’ve been in the heavy equipment , and heavy hauler side for the biggest part of 20 years

 

Hard to say,describing sounds over the internet is pretty tough without a video attached.
Plugged cat? Timing chain/belt jumping? Electronic engine controls? Fuel delivery issue?
Could be a lot of things based on that vague of a description.

 

yeah I agree I like to have as much info as possible when I get it back together i will try to post audio or a video or something but here is a little more history on the car my wife got it from her cousin, her husband put another motor in it cause the one that was in it when they bought it came apart, this motor only has about 60,000 miles on it since rebuild! (Well since it has had new gaskets put on it) I’m sure he didn’t replace any bearings either way thanks for the reply I will try to get that video loaded up ASAP. If you have anymore question about it I’ll be glad to answer

 

does it do it all the time while running, like when in park? going to have to find where its coming from if you can. plugged cat comes to mind and could make engine knock but it would not be all the time, more when throttling up.

 

Yes it makes the sound all the time, kinda quiets down after initial start up about the time the rpms stable out but when rpms increase so does the noise, I believe I got it narrowed down to the water pump that’s where the majority of the sound is coming from (well that area) used my stethoscope on it and that is where it got more defined, I’m figureing it’s eithe that or deeper in the motor right now a water pump ain’t looking too bad! Lol

 

unhook the fan belt and see if it keeps doing it. that would rule out anything hooked to fan belt. dont run very long without it.

 

The way you described the running problem that comes and goes sounds all the world to me like a timing chain jumping and that would be right behind the waterpump.

 

Yeah I removed the water pump today but it wasn’t the cause of the noise the bearing wasn’t too bad but it did have a little wiggle and endplay to it so I went ahead and changed it, and I believe you are correct on the timing chain either that or the balance shaft bearings are going out if that’s the case machine shop hear we come

 

I do apologize for the delay in checking this post been stupid busy, so an update before I started tearing the motor down I put every little thing back in place in order to crank it and listen one more time! And I can’t remember it I mentioned my stethoscope in previous post or not but anyways I used it to try to isolate the sound a little and it was the loudest directly behind the water pump teardown begins finally on top of everything else tear it down looking at the timing chain and all the goodies behind the front cover and everything looks good!! Oh Joy! Any ideas! I’m starting to tear down the top now figure I’d work my way down I know limited information is a big factor on this thread and I do apologize for that also but putting the take off part aside the knock(rubbing sound)was a new thing it didnt sound like lifter valve but it looks like we will find out!

 

God luck,starting to sound expensive.