Have some one drive it an walk beside it and see if the shanks are flexing or if it is the springs. If it is the shanks than you are either too deep for the machine, ground hard, or running too fast for the conditions. Remember these machine where designed when we where chiseling at 4-5 mph. Now we have bigger MFWD tractors so we are running at 6-7 mph. Watch and see if all the shanks are flexing at the same time. I have seen this make them just about hop out of the ground.
IF it is the standard springs then check and make sure there are not any broken ones. They also loose their strength. You may need to replace them.
Is this machine new to you??? Is this the first year you have used it or is this just the first time you have had the problem?? The reason I am asking is that the ground is dryer and harder this fall than normal. I am running a gear lower on my JD 4960 than we normally do. I also have noticed that the shovels are wearing faster. The ground is like concrete in places.