Noise cancellation for electromagnetic signals
Twisted pairs(usually with differential signaling), common-mode chokes, ferrite beads, decoupling capacitors, shielding are common solutions. It is difficult to address your problem without the exact setup and attempts to solve the problem, but I would like to add to the above comments with some good shielding practices, since that is the solution you are using.


When shielding, grounding on one end will only help against interference from electric fields. Grounding both ends will help against both electric and magnetic fields, but will introduce ground loops, so extra measures must be taken to prevent/compensate these(you should try to ground everything to the same reference point in a 'star' grounding configuration andyou should try to keep the enclosed surface between shield and ground as small as possible).
Prevent grounding your shield with a long wire (pigtail grounding), because this wire itself can radiate EMI.


Shielding done wrong can actually backfire, so I would personally use twisted pairs as a starting point against EMI.