In the past, the sound of piston slap meant trouble. Worn cylinders, damaged piston skirts, or cracked pistons were common causes, and all meant expensive repairs. Now things have changed.
Engine designs have changed to make them more compact, lighter, with less internal friction, and higher revving. To do all this, piston design had to change, and some of the major changes are shorter piston skirts and straight piston skirts. The short, straight skirts allow the piston to rock more in the cylinder, and we hear it as piston slap.

Closer manufacturing tolerances have helped reduce piston clearances and slap, but some engines need more piston clearance to allow for piston expansion. During the first few minutes of operation, the piston can expand several thousandths of an inch, yet clearances are typically in the one to two thousandths of an inch. Fortunately, the cylinder also expands, or we would find pistons seized.

On vehicles built in the last decade, piston slap that occurs for a few seconds on cold start is quite normal. From experience, I have found that piston slap that occurs only during cold starts and lasts only for a minute or less causes no problems. Just don't place a load on the engine until the pistons have expanded and the clearance has been reduced.

Here's a service information notice from General Motors. Itstates "A cold Piston knock which disappears in 1.5 minutes should be considered acceptable".

 

Well, the STP didn't work like I thought it did and would it workon piston slap?The noise is the same. Here is a better sound bit.Is your thinking the same? Again, it's 30 seconds in.
Thanks
http://www.youtube.com/watch?v=8d9FAL_1jLc

 

I still am thinking piston slap. The tone of the knock is to high to be a crank bearing issue. It could be the lifters bleading down, but the noise is a fariable frequency and moves around the engine. Also, lifters normally are more if a steady cycled "Tick" until they are fully pumped up. I personally would install a machanical oil pressure guage where the sending unit is and then do a cold start to see what the pump is producing pressure wise when the noise is occuring.

Does itproduce the noise after setting quite a while, but the engine is still warm?

 

Sense,
I'll try checking the oil pressure. It has of late been making the noise after only sitting a short while. Thirty to fourty-five minutes sometimes.
In the mean time, here is another sound clip. On this one I put the truck in gear and it changes the sound of the noise. Hopefully this will help some one down the road not have to go through weeks of trying to figure out a strange noise.
Thanks ,
Dean
http://www.youtube.com/watch?v=1LWVtifr4Fs

 

It ended up being an exhaust leak at the rear of the head/manifold gasket. Ireceitly met aMarinewho happened to just get back from an Iraq tour and who happens to be a diesel mechanic. He noticed it right off as an exhaust leak. I payed him to fix it. He did it right there in the RV park.
If you notice on the last sound clipwhat some mechanics weresaying that my starter was hanging up or releasing slowly. That noise too is gone.
My truck runs smoother now and idles better too. What a big diffrence.
I spent the past two monthsin the trailer next to this Marine while in Galveston andam grateful for men like him protecting our country.
What luck! I've been banking my head against the wall on this for months.