M-audios tech support does not have the best reputation. These boards are aimed at a market where the user has a lot of knowledge on configuring a pc - or visits these forums for help! All the Delta range have excellent audio performance but it only comes on a well configured pc.
The Montego is pretty good but is a Windows sound card - No ASIO or GSIF drivers that many pro applications use. The more recent Santa Cruz is a better card and will give a better combination of connections - choose 4in 4out, 4in 2out + headphones, 2in 6out or 2in 4out + headphones. No digital in and the digital out is only for surround speaker sets. Still only has Windows drivers though.
As for noise, the only part of a modern Windows card that might be expected to noticably suffer this is the mic input - best to use an external mixer or pre-amp and avoid the mic in in favour of the line in. A few more causes might be A, The s/card is picking up from the video card - plug it in the bottom slot. B, The back panel screw is loose causing a bad ground. C, A midi daughterboard synth is plugged in and causing ground noise. D, An unused input is turned up in the cards mixer control.
The Delta cards don't have a midi synth or daughterboard connector and neither do most similar ones from other brands. A few exceptions I know of are STAudios Media 7:1 and
the Terratec DMX 6Fire (doesn't come with a synth, but does have a daughterboard connector). It's best to fit a pro card in addition to a Windows card like your Montego unless the pc is exclusively for Music production when a Windows card would be unnecessary.
A good (free) program for testing a cards sound quality is the "RightMark Audio Analyser (RMAA")...
http://www.benchmarkhq.ru/b_e.html#rmaa
You need a stereo mini jack to mini jack cable to connect the line out to line in for the prog to work.