Is there a way (other than opening the board) to tighten the modulation wheel? I play pretty hard and sometimes it will move.
You need to get a solid stand - one that absorbs the shock without moving. There is nothing really to tighten. If playing the keys moves the wheel that's intense... ensure your stand is rock/rock solid. Which keyboard do you have, CP4 or 40?
CP4
If this continues as an issue, try placing the CP4 Stage on a rock solid surface, unless you are hitting it directly with your hand or wrist (which is a possibility), the MW should not be moving. If the change it causes is unwanted, you may wish to deactivate the MW in that particular Performance. This way if it does move by vibration or direct contact, it will not impact your playing.
The first time I noticed it, I was on my Freedom SolidStand. That's about as "rock solid" as you can get. I guess I'll keep a little wedge at the back to prevent it from turning.
If you program it to do nothing, you don't have to worry about it. You may want to GoPro yourself playing just to see if you are hitting it while performing (so you know for sure).
There's no way I'm hitting it, so I'll program it off.