Exhaust Leak Maybe?

No, it would not necessarily throw a code.

It would sound like a ticking sound that gets louder under load or throttle.

tick, tick, tick.

Have you checked your EGR Tube as well?

If you smoke cigars, you can always get up under it and (weather permitting) blow a cloud of smoke up there, and if there's a leak the cloud will visibly move one direction.

CEL's can pop up if it's a leak before the front o2.

sounds like a exhaust leak to me. check the egr tube, sometimes they crack.

ya know ive got the same problem... so i got complete new exhaust and still have the same noise. only when you raise the rpm a little or if it sits for a few minutes. i was told plenty of times that it was the lifters and how oil isnt getting to the lifters...


Jake

Run some Sea Foam through the intake. It will make your car smoke like a train for about 10 minutes while it cleans the upper part of your engine. Any leaks will become obvious. That how I found my exhaust leak. My crossover pipe was split right along the weld on both sides but I couldn't see it because of the heat shield that was tack welded around it. It took less than 5 seconds to find that leak once the smoke started.

Here is a write up by a friend of mine who has a 96 Cobra. He does all the work on my GTP.

Courtesy of stampede3...

Seafoam does a good job of cleaning the intake and cumbustion chambers. I normally don't like to do it on roots or twin screw supercharged cars due to the close tolerances of the blower. It can be done but you must be more carefull than on a N/A car because your sucking a liquid through the blower.

First I recommend you get a small drinking water bottle (16oz) and empty it, fill it halfway with seafoam. This is only so you can see how much you are sucking and how far down to stick the hose.

Find the big vacuum line off the intake that goes to the brake booster. (right above and behind throttle body to the booster)
Next you will need another piece of vacuum hose (about 1.5-2 ft long) that will fit inside of your brake boosted vacuum line. Must be a tight fit.

2 people make it eaiser but you can do it alone. Start the car, pull the hose off the brake booster, stick the smaller hose inside the big one.
(When you pull it of the car will stumble alot, you may have to cover the end of the hose for a second so it doesn't kill, if you have 2 people you can put the hose set up together first, hold you finger over the end and have the 2nd person start the car)

Have your bottle ready, tilt the bottle at a slight angle (about 30deg)
Start to stick the open end of the hose slowly in the bottle.
(DO NOT JUST SHOVE IT DOWN IN THE LIQUID)

As you get close to the liquid you will see the seafoam start to swirl around in the bottle. You will be able to tell when it starts sucking in, the motor may rev just a little bit and or my stumble worse.
Move the hose in a little further and pull back, keep doing this over and over, Kind of in and out, in and out, if you know what I mean. LOL

I have every so often stuck it very very quickly into the liquid for a split second but don't recommend it unless your comfortable doing it.

After a few min. of this it will start to smoke pretty bad out the exhust. at this point continue until the bottle is empty or stop and kill car.
Then hook vac. lines back up normal. let car sit for 15-20 min. then start. It will smoke like a train for a while, rev it a few times or go drive down the road and you are done.
Repeat the whole process again if you want, I use the whole can for a treatment. some only use 1/3.
It may throw some trouble codes in the process so you will have to reset the computer when finished.

Buy a can of sea-foam and run it through the engine vacuum lines. Not only will it clean out the engine, but you'll see smoke coming out of any potential exhaust leaks...

I did that and it smoked like crazy but I still don't know from where...