For effective
magnetic shielding you have to use something like an iron-nickel alloy or mumetal to construct a box to put it in.
If it's an EMI/RFI problem, then you can put it in a copper or copper plated enclosure (basically a Faraday cage). If the EMI/RFI is the problem and it's reaching your monitor through the power connections, then you have to put filters on the power to pump or run it off a seperately filtered supply.
But a far easier way is to move you monitor farther away