cmartyn wrote: ↑Fri Jul 15, 2022 9:28 pm
By subframe you mean the big squareish welded steel structure that the torsion bar is bolted to correct?
Correct. It basically attaches the engine and front drivetrain to the car as a unit, and acts as a leverage point for the control arms and sway bar.
cmartyn wrote: ↑Fri Jul 15, 2022 9:28 pm
You would think if that was loose it would make all kinds of noise all the time.
Not really. The weight of the car is on it, so unless it's really flopping around, it takes some force to get it to shift position. The sprung components don't generate those sorts of forces in and of themselves simply because they're sprung, and forces from the rotating components exert themselves indirectly via the engine. So torsion on the body is the primary force that can actually load and unload it and cause it to shift. One of the toughest "clunk" cases I ever worked on (a loud, infrequent bang just like yours) turned out to be a rock caught between the body and a subframe back bushing on a gen5 Altima. It seemed to come from the firewall near the driver's feet, and after literally tearing out the dashboard and driving the car around with most of the interior missing looking for loose seams, the evidence fell out in our laps when we dropped the rear bushings on the subframe. In the immortal words of Charlie Brown, "I got a rock."