07musclemustang

there can still be some detonation.
i would be betting on heat shied from exhaust

Sirsilent

I wish I would know how spark knock sounds... it does not happen in ide, just when driving

MrSandman

Engine knock sounds like a rolling bag of marbles... and happens in each gear.. when ever the car is pushed.

The sound you are referring to is either of these known issues:

The spacer plate between the transmission and the engine

"4.6L MANUAL TRANSMISSION - SEPARATOR PLATE BUZZ - BUILT BEFORE 12/13/2007
08-2-4"

or

The transmission crossmember. The crossmember is the aluminum brace under the car in the area of the center console. The crossmember itself can be loose, be on backwards, or the exhaust hangers on either side are causing the vibration. These are all known issues and are highlighted by Technical Service Bulletins.

"RATTLE/BUZZ/VIBRATION - TRANSMISSION CROSS-MEMBER EXHAUST MOUNT - BUILT BEFORE 12/3/2007
08-2-10"

"SHUDDER ON ACCEL - POSSIBLE WRONG TRANS CROSSMEMBER ASSEMBLY INSTALLED (EXCLUDES GT 500)
08-21-7"

The exhaust hangers are not functional, and were placed there for manufacturing purposes. If the metal hanger coming out from the exhaust pipe is pressed up against the hanger, a vibration can occur.

The crossmember itself is swappable from the v6 to the gt... except that it's in an "upside down" position on the V6. If this was installed improperly from the factory, it could cause the noise you are describing.

The bolts themselves that hold on the crossmember can also be loose.

Sirsilent

I flashed the 87 tune today and drove it with 91 fuel. No rattle or pinging anymore so it must be the 91 tune. And I thought the 91 tune is made for 91 gas...

07musclemustang

is it a custom tune??? If so email who you got it from and they'll make an adjustment.
not all 91 octane is equal, time its spent in the tank (underground), quality, sharing lines, ect can lower the octane, generally speaking the octane you put in is usually less then the pumps say by 1-3 points.. sad to say.