What sarcasm? Looks like he got some pretty solid answers.

 

x2

 

what solid answers???????????? percussion pistons or straight sixes never have a piston slap?????????????????????????????????????????????? ?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ?????????????????????????????????????

 

You seriously took offense? It's not even your thread and the OP obviously took the comments for what they were. He laughed at the percussion slap and the other guy did not say they never have piston slap, he said they dont have much piston slap. There are guys on here that will pick you apart for saying somthing dumb and I am the first to stand up to that, but these post were obviously just for fun. Chill!!!!!!!!!!!

 

get a big screwdriver or one of those mechanics stethascopes and see where the noise is coming from. mine sounds like that too and i think its a oil delivery problem in various points of the motor. like the lifters maybe?

 

I added a couple more videos to help with troublshooting.

Here is a video of cold start:

http://www.youtube.com/watch?v=http:...?v=I4MhD5I52rM

And here is a video of the knock after taking the jeep for a ride.:

http://www.youtube.com/watch?v=http:...?v=6oXwyrJXTXk

I rev it a couple of times too. Please let me know what ya'll think.

 

Hard to tell with out being able to locate it with my own ears, mic on a camera dosent tell you which way the sound is coming from. Its an auto I assume? Have you looked at the transmission for the source of the sound? I could hear it, but dont recognize it and cant pinpoint the area its coming from.

 

It is an auto. It sounds like it's coming from the rear of the block or bell housing area. I checked the flex plate bolts though and they are good.

 

I hate to say it, but, im stumped. You may have a "death rattle" beginning.

 

What is this "death rattle"?

 

The last noise a motor makes before it craters. Not trying to scare you, but that is what I can make of it out of what I hear from a youtube video with earphones on. Not a final verdict by any means, you are more than encouraged to get a second opinion. This is kinda like going to WebMD to diagnose cancer.

 

What's weird is that it's a brand new motor. Has about 900 miles on it.

 

Just from what I can hear, it doesn't sound that bad....hard to tell thoughover the internet. Sounds like a lot of engine noise transfered through the exhast. The 4.0 can make a lot of noise for a longtime with no adverse effects on perfomance. I'd drive on.....jmo though
Good luck!

 

Only 900 miles? Hmmmm... You may not have a problem then. Is there any checks you need to do after the break in period? Knowing it was a new motor would have helped from the get-go though.

 

Take a vacuum hose about three feet long and tape a soft wire on the end as a wand leaving the end open put the other end up to your ear and check around the exhaust manifold donut and where the pipes are welded together. Mine had a small crack where they were welded and after it got good and hot the crack opend up and got louder sounding like a knock. And yea it went away or at least it sounded better at higher rpm`s. The vacuum tube stethescope trick also works for pinpointing vacuum leaks as well. My guess is a cracked exhaust manifold given the location of the noise. The vacuum hose will confirm and pinpoint any exhaust or vacuum leak. If your lucky it is just the donut.