Yo. I dig my ford.....But so far the engine has not been that great to me.

1st it used to burn about a quart every 1K till I started to use Ams oil 0w-30w extreme service oil. Now it only burns when I work it.

2nd....and most importantly (I can always add more oil) It knocks....but it almost sounds like a scratching sound. Only when I get on it. If I take off at 1/2 throttle or so....it makes this noise from the engine. It is not consistent. If I keep the foot at the same position on the throttle, then it comes and goes as the engine gains RPM and speed.
Other than that. She runs great. Always has. I got her with 69K. I have 89K now.

2002 F-150 Lariat FX4 Screw
5.4 V8
Airraid cold air intake
Flowmaster 70 series exhaust system
TB spacer (I think I need to take this out, it whines and it has the cuts in it for the tornado effect,I heard those are the worst????)

Edge Programmer (Yes, my truck makes this noise without any kind of tune...Makes noise on stock setting,. Infact when I use the Performance lvl3 setting it makes the noise happen A LOT more.

BFG AT 35" tires
4.56 Gears
stock LS rear

and LOTS of other stuff that has nothing to do with the engine making scary noises.

I tried to even use the edge to turn the timing down -5. It does not go any lower and my truck STILL makes this noise......

I had a tune up done about 3K, ago....The plugs where done....but no the C.O.P.S. Maybe I should have done the cops......

I'm freakin out!!!! Why does my truck sound this way!!!

BTW the gears are worth the money. I love them. Better then everything else performance wise, put together....

 

Could it be a vaccume leak? the way you describe it, it sounds like it happens in a high vaccume situation. When you floor it, the vaccume in the manifold drops, when you let off some, the vaccume will raise fairly quickly, maybe that situation reveals a leak of some sorts, just something to think about.

You can pick up a vaccume guage quite cheap, get a nice length of hose and put the guage in the cab, you should be able to see if the noise corresponds with the vaccume guage movement.

Otherwise, maybe check the alternator, try turning on and off heavy amp drawing accessories and see if it changes the sound. Also, how about belt condition, or idler pullies? Wish I could be there to hear it, its hard to diagnose a sound over the net!

Josh