Noise from the engine/transmission area

[SoundEfx]

I have a 1997 Exp. XLT V8 5.0L 130,000 miles, that make a rattling noise when driven.
If I put it in Neutral and rev the engine, there is no noise. It also does not exist when I have it in the lower gears (2, 1.) It only occurs when I have it in Drive (D.)
Does anyone have any idea on what the noise can be and a way to fix it?
Also, can anyone give me some tips on changing the spark plugs and wires on this engine. Ford found the most difficult and awkward positioning for them and they seem very hard to get to.
Any tips or suggestions will be appreciated.
Thanks.

 

[Dopler174]

It could be the heat sheild around the catalytic converter. OR it could be the flex plate cracking and exploding.

 

[d4rizob]

You can get to the plugs easily if you jack up the front, take off the tires, and pull the splash guards off. Easy access.

 

[SoundEfx]

Thanks for the replies.
I will try the remedy for the spark plugs, but I have another question and try not to laugh too loud.
What is a Flex Plate and where is it located?
Thanks again for your help.

 

[d4rizob]

hahahaha, flex pate is the flywheel, between engine and transmission, bolts to torque convertor,thats what pictured above.