Identify my engine noise

[SciFiHiFi]

My motor is making a loud noise, similar to a rod knock.
It only occurs when the engine is hot, and has just been driven.
The knock goes away after the car idles for a few minutes, and returns after the car has been driven again.

I have checked all the easy stuff:

Oil and coolant - clean
Plugs - clean
Data log - everything looks normal
Performance and driveability - great

All of the pullies are quiet and tight all though I have not gotten to those secondary accessory belts.

Any advice on what to do next? Is it time for a compression test?
I was going have a look under a valve cover but I don't really know what I would be looking for.

Car info: early 03 cobra, 36,000 mi, 2.8 pulley, LDC head cooling, a bunch of other mods that aren't relevant to this issue.

thanks

 

[T-Pain808]

Video with sound would help, what weight of oil are you running.

 

[SciFiHiFi]

EDIT: apparently the forum automatically embeds youtube videos. They're not working for me like that so you may need to click the title at the top of the video to launch it.

Video with sound would help, what weight of oil are you running.

5w30 synthetic

Video 1: [ame="http://www.youtube.com/watch?v=NOXkjUH_XaE"]YouTube - knock[/ame]
noise can be heard from the start until about 11 seconds. It is most pronounced after the rev when the RPM's are falling.

Video 2: [ame="http://www.youtube.com/watch?v=nfs7PdvJ9Yo"]YouTube - cobra knock[/ame]
The exhaust drowns out the noise in the video but in real life the knocking is quite loud.

 

[forcefedcobra]

its hard to tell by the video. I have a knocking noise that is louder sometimes and quieter sometimes but goes away when the motor is under load and comes back when the load levels out. It is easily heard from around the back of the blower but is loudest under the car near the bellhousing.

This weekend we will be pulling my motor and installing a new aluminum longblock. When we get it all apart if we find something I will post back. We are thinking it is a burnt piston skirt.

 

[T-Pain808]

It is hard to tell from the video, I would say if it was a rod knock or the tick it probably would be louder.