soundcards from asus seem to be the hot pick nowdays. i used to use soundblaster however i've heard they arent so great anymore. sorry i dont use a soundcard anymore so i cant give you specific examples of what works good and what doesnt. i jumped off the soundcard boat years ago and everything is processed by an external DAC (my receiver)
potential cards:
the asus xonar dgx is only $25 with MIR right now. the next step up would be the xonor ds which is $43. they get average reviews. the cheaper one is better than the cheapest onboard sound but on par with decent onboard. the more expensive one is just a tad better than onboard sound. any slot card should have a bit less noise than onboard sound though.
http/www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=-1&IsNodeId=1&Description=asus%20soundcard&bop=And&Order=PRICE&PageSize=20
potential external:
creative go $40 doesnt get a bad rating and is small with only a headphone jack for 2.0/2.1 systems or headsets. this should have even less noise than internal. *should* being the key word.
http/www.newegg.com/Product/Product.aspx?Item=N82E16829102036&SortField=0&SummaryType=0&PageSize=10&SelectedRating=-1&VideoOnlyMark=False&IsFeedbackTab=true#scrollFullInfo
as for speakers... perhaps:
logitech z313
creative a220
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now those arent super high end soundcards however if your issue is just electrical noise from your motherboard any slot or external soundcard should help reduce or allieviate the issue. this will not help if the issue is external (ie something sitting on your desk or dealing with your wiring, etc)
those speakers arent super high either but are not half bad. my mother and uncle both have a pair and love them. i've never heard static on them the few times that i've used them or heard them. although i've never really heard them 100% maxed out (which is not adviseable in any case). so cant say say if they have any speaker hiss at max or not.
no, i dont think the cables going to the speakers are going to have any sort of thick shielding on them for the price. however if that is an issue then perhaps you need to look around on your desk and see whats generating the electrical noise.
keep in mind that such things as cell phones, chargers and in some cases wireless sources have been known to cause interference. do you have a phone, router, charger block (transformer) or other such object anywhere near your speaker wires? (or even the ac wire for speaker sets) ?
i still think that the issue might be some sort of interference generated in your desk area or perhaps over the ac lines. if thats the case then a soundcard and new speakers might not fix your issue entirely but might offer some improvment at least.
i really cannot with 100% certainty, promise you anything.