What gear and at what RPM?
If you are in the wrong gear (too high a gear and too low RPM`s) and it doesn`t do it when in a proper gear, well,, I think it`s obvious as to the cure.
Have you ever seen what the motor does when in the wrong gear? It wiggles and squirms like a stuck pig. This, in turn, rattles the whole exhaust system and drivetrain and somewhat the whole vehicle.
The rattle you are trying to find could be one of many things with part of the exhaust system being the more likely culprit (including hangers) but the actual culprit is being in the wrong gear for your road speed (ie, RPM range).
With my 16vlv 4dr 5spd, I can have low RPM`s (near idle speed) in first and second, but as I climb up the gears from there, 1500 RPM or above is needed if I want to accelerate without lugging (shake, rattle and rolling) the engine. In fifth I like 2K RPM as a minimum. More-so, if I am facing uphill.
There is a difference between bogging down (engine malfunction) and being in the wrong gear.
If you just want to find the rattle so you can fix it, put your E-brake on hard, choose second or third gear and try to `go` with someone under or nearly under to help listen to where it is coming from. Be very careful not to run helper over!!!
I have also brought the bumper (non-airbag car) snugged up to a brick building (or other strong resistance) and used the wall as a stop under acceleration to be able to apply drive train torque to find issues such as U-joints or other clanks or under load engine issues... You could also use safety tow chain or strap if need be. Just be careful, try first without anyone under.
