I have a 2001 Pontiac Montana experiencing the same noise, like a pop of a joint. It only occurs on very sharp - 90 degree - turns, for me to the right. It does not happen as often if I am coasting into the turn. I am also experiencing the following:
(A) Very shrill “nails on chalkboard” grinding when applying the brakes. It does sound like it is coming from the back of the vehicle. Not sure though.
(B) “Chirping” noise from the passenger side under hood. Almost sounds like behind front passenger side tire. All belts were changed and re-changed. They can’t seem to locate the chirp. Good thing is that it scares deer.
© On occasion - very little - the van shifts very hard from third to fourth. This happens most if I am driving from interstate to back roads or have been parked in idle for any length of time. Some bo-zo mechanic said a Pontiac takes time to get “use to the driver”. It started after a lengthy repair where the computer & battery were unhooked. Anyway the idiot told me that it should “work itself out” well, now a year later, it still happens.
On your first question. Have the front suspension/steering components inspected. The popping noise could be from a worn ball joint or broken stablizer bar end link.
(A) Have the brakes inspected. There are wear indicators on the brake pads that make this noise when the brake pads become worn out.
(B) Have the serpentine belt removed and then operate all the pulleys by hand. This noise can be caused from a worn bearing in one of the components the serpentine belt drives. ie: tensioner/idler pulley.
© When was the last time the transmission fluid was serviced?
Tester
Too many issues not enough info. When was the last brake job(in miles). When were the ball joints inspected( state inspection?). What does the trans fluid look like (clean or dirty). How many miles on the car. Chirp is likely an idle pulley and if the belts are new turn up the radio(could be an alternator pulley). All cars these days use a transmission management computer but this shift is not likely a problem if you have low miles and good trans fluid. There are sensors in the transmission that could cause the problem of a hard shift. These are not too expensive to replace but if they only cause a problem infrequently a scan may not show the problem.