why is my 4.5 engine making a clicking sound when i accelerate?

It could be many things, unfortunately and without hearing the noise first hand or being able to do some basic diagnostic tests or be able to drive the car, its hard to say what the source of the noise may be. It could be flex plate issue but hard to say without being able to hear the noise.

As stated, hard to give a real diagnosis w/o driving it. I am a DIY guy too and it sounds to me that when you put it in drive car is now under a load. this would lead me to thinking possible u-joints, or drive shaft issue. The way I save money and get a good view is I go to a used tire and muffler shop. I tell them it's making a noise, maybe the muffler ???? they will put it on lift and you can examine under carriage and they will help. I have never been charged, and if you find what's wrong they can probably fix it.