Unsolved rattling when accelerating and engaging clutch


I have a strange rattling sound that started about 10,000 miles ago in my 2005 corolla with 133k miles. I thought at first that it was something loose in the wheel well. This does not seem to be the case any longer. It rattles when i engage the clutch upon take off or any time i accelerate when driving. There is no rattling at all when i rev the engine or at idle. It does not rattle once the car gets up to speed. I do not notice it particular to any RPM. I thought it was the throw out bearing but it does not rattle when i put the car in reverse and accelerate in reverse. It seems to rattle also when i drive over rough terrain. I have tried jacking up the car and looking for loose hardware with no luck. Heat shields are solid so could it be suspension? I have had a mechanic look at it and he thought it was an exhaust leak but now he's not sure. Please help!
Sway bar links seem to be solid. Have not looked at suspension arm yet. I'll look at the engine mounts again but they seemed to be good.
Once I had a horrible noise below, apparently pass by a stone road and the stones got between the suspension arm and the chassis of the car and made a noise as if something was going to come out
I recently lost a 12 mm socket. Maybe this could be the culprit. Still have never found it. Would make my day if i could find my long lost socket and repair a rattling sound at the same time!