Click Click!

[my9250GT]

I have a 92 GT with bbk equal length headers,bassani x-pipe w/ cats, flowmasters, eibach springs(which lowered the car about 1 1/2 in.) and some other stuff that is not relevent to my question..I recently got all this stuff installed and on sunday i started to hear a "click" or "knock" comming from underneath the car. it only happens when i step on the gas if the clutch is pushed in and i am coasting and i step on the gas it does not click! it only seems to do it in gear and only after i press the accelerator but it only does it once, if i let go and step on it again it does it.it is really starting to annoy me! if anyone has any clues to what is causing it please post...also i lifted the rear end and put on jack stands then i put it in gear and hit the gas and no noise....