If you don't have a interface and looking for something to get rid of it try
Two 2 in Line RCA Audio Noise Suppressor Filter XR 16 Ground Loop Isolator | eBay I used that when I was in your position before. Also CRT monitors are trouble.
TRS to 1/8 Gold
5 ft Foot Adapter Input Cable Cord 1 8 TRS 3 5mm Stereo Plug to 2 Male 1 4 Mono | eBay
I would make sure they're shielded.
This is also good
6 ft Feet 1 8" 3 5mm TRS Splitter Y Cable to Dual 2 XLR Male Adapter iPod MP3 | eBay again some shielding would be better...But RCA is the weakest link in all cases...The line isolator did the trick for me then though. Simple Trip to Radioshack you can find all that stuff except an interface.
If you had a interface XLR to XLR or TRS to TRS are you best bet. Depends what your Interface support's most interfaces will have TRS ports these days though if it doesnt have XLR outputs. If you see on the package "for guitar" just disregard that a lot of sellers don't advertise other purposes that the cables can be used for such as monitors, interfaces, mixers, patch-bay, microphones etc. When buying the cables also try to keep in mind gold, shielded always.
Another tip is sometimes 3 prong to 2 prong adapters at the bottom of your monitor plugs to your outlet as in speakers or screen can eliminate a hum.