Thought I'd share this in case anyone else has a problem in the future and the search turns up nothing.

I have had a 'popping' noise coming from the front left corner of my 240 for days, along with a clunk felt in the floor pan under my left foot. This only occurred on braking, at any speed. I could not reproduce the noise with the car off, so I suspected ABS issues (I also have an intermittent ABS light). Cleaning the sensors did not help, nor did disconnecting them, so I jacked up the car to inspect the suspension, even though I couldn't fathom a problem there; all bushings are SuperPro polyurethane, ball joint and tie rod tight, and the strut mount is in good shape, and recently tightened.

Apparently the cause of the noise was the blue poly sway bar endlink bushings which had split (the little donut bushings which sandwich the sway bar - Mmmm, donut sandwich). I replaced them with old rubber bushings and no more snap, clunk, or pop.

Odd symptom for a sway bar endlink, and I never would have guessed it was anything but the brakes. In most cases, I would have guessed a control arm bushing, loose caliper, sticking guide pins, loose strut mount, etc., but all of those things were perfect. Go figure.

Hope this helps somebody one day. I'm still confused by it.

-Sean