I have had to tighten many donut rubber posts on almost every NIB STERN I have purchased right out of the box. Not your issue but I totally get it . If you post some photo's that will be helpful . Use you finger or something and point at each part that is rattling loose . Is it the wood screws ? to playfield I have a fix for that . Photo will really help and also if this happen to others we will have some documentation .

Its the screw on the bottom of the plunger that rattles loose. The cap (?) and the spring pop off and are laying in the bottom of the box. If we take the wood screws out and totally remove the plunger assembly, it works fine manually. Nothing binds on the white plastic, the spring pushes the plunger back smoothly, etc. The problem begins once we screw the assembly back onto the playfield. I assume the assembly isnt exactly aligned with the two holes in the playfield, as it starts to bind horribly. If I tighten up the 3 wood screws, and the 2 screws on the plunger assembly, I can barely even get it to move in or out of out of the hole, thats how bad its sticking. One thing to note is that in switch test, the coil gets very hot, almost like its not popping and releasing. More like it's staying engaged. I expected it to push the plunger up and the spring pushed it back down. Not sure why it would get hot. Maybe something with the coil? Hope that shines some light on the subject, thanks in advance for the help.

Did you ever fix this? I had one of the posts fly out today onto my playfield. Found the screw in the cabinet and put it back on but now it’s binding just like you described. It pushes up okay, when it retracts there is some tension in the coil preventing it from completely going down. Worked perfect before the post flew out. All the screws into the playfield are tight.