What's that knocking noise??
 

First started noticing it about a week ago or so. It is not audible from inside the car. But from the outside sounds like its coming from up by the converters along side the transmission/oilpan area. Can't see anything visible as far as exhaust leaks/anything banging into stuff. You can hear it from the engine bay too, but it doesn't seem to be as loud there. Could it be a lifter?? Problem with the transmission?? Simple exhaust leak that I'm not finding?? 02 sensor noise?? The knock increases in frequency along with the engine revs, however it does not get any louder. Oil level/pressure is normal. Car seems to run normal. But its definately the loudest from underneath the car up around where the transmission/oilpan are. Any ideas???

Ttt...

Exhaust leak sounds the most likely, especially given the area. They are fairly easy to spot though, you'll eventually see black soot in the area of the leak. Maybe try cleaning everything up as good as you can and then check a week later?

Only other thing I can think of is a cracked flexplate. They usually tick. However I believe they are generally much louder (audible inside the car).

Dope

it is probably piston slap which is a serious warranty issue GM refuses to address... you should join the class-action litigation against the General....

My car is a '98, so I doubt its piston slap. I'm thinking exhaust leak to, given that you can only hear it when your in the car if there is another car next to you, or if your up alongside a building.

Heh, my 98 actually does that too. You can see the soot at the connections too. I tried tightening the clamps and it helped 75% but you can still hear it when the car is cold and next to a wall. Someday I'll get off my rump and get all the connections welded up.

Dope

Knocking Noise
 

About a month ago I noticed this knocking noise coming from underneath my car. I figured it might be something to do with the exhaust, since I couldnt' hear it from inside the car. Well I finally got it over to my mechanic and got the car up on a lift and it turns out that its coming from the top end of my engine. Back by cylinder number 8. He thinks its probaby a rocker arm, or maybe even a lifter, but most likely a rocker arm. The knocking has been going on for about a month and hasn't gotten any worse or better. So has anyone had this happen to them before??? How hard is it to get that valve cover off and replace that rocker arm?? My car has 80,000 miles on it and is relatively stock. What might have caused this problem in the first place??

Ttt..

on your car its just a matter of unplugging the oil pack harness, removing all 4 pks individually & taking off the 10 or so bolts holding on the valve cover...its a pita on 98's but still not difficult and should take less than 1/2 hour IMO to get it off.

Well, who knows if it is the rockers. Just called a local dealer and they don't even stock, or remember ordering rockers for these cars cause they never go bad on a stocker. So now, after talking to another tech, he thinks it could be one of the valves slapping, which would involve more than taking off the valve cover, more like taking off the head. WTF??? How would this happen just all of a sudden on a stock car that hasn't been beaten on much.

Take off the valve cover and take a look. Pushrods are probably the most common cause of under hood tapping.

Pull the rockers and pushrods and roll the pushrods on a flat table to see if any are bent. If you find one (or more) that are bent. You got off easy. They are inexpensive and easy to replace.

Just got back from taking my car down to a former chevy mechanic's shop. He said that its definately something coming from up top back by the #8 cylinder, but that he wouldn't know what it was until the valve covers came off. He said that he's never even really worked on an LS1 before cause they basically never came into the shop. Gonna go and get a service manual and get the valve cover off and take a look

Yeah, about that knocking noise.
 

Okay, so I posted here a few days ago about a knocking noise my car was making coming from underneath. It had been doing it for a little over a month. I took it to two technicians who both determined that it was coming from the top half of my engine, towards the back passenger side, most likely a bad rocker arm or maybe even a valve problem. So that sucked, and most of you on the board came to the same conclusion. So here I go buying a new rocker arm, pushrod, and valve cover gasket, all ready to take the sucker apart. So I'm driving home and I notice something. While listening to the radio, the signal got a little static, and that static sounded a lot like the pattern in the knocking. I revved the engine, and sure enough the static increased with the rev. Holy shit!! So I get home, wait for the car to cool down, and start going after that #8 plug wire. Sure enough, the spark plug ends up being lose by about half a turn. I tighted it up, took about a freakin' hour, put it back together, cross my fingers.....no knocking!!! Car runs perfect!!! Guess I'll be returning those parts thank god.