High pitch sounds out of power supplies usually indicates the transformer windings or plates are vibrating - the resin used to bond them has broken loose. In minor cases, it is nothing but annoying. But in extreme cases, it can affect the electrical characteristics. But in any case, it should not manifest itself into something you can hear through the speakers - as that indicates there is some sort of electrical interference or improper crossover involved, and that is not good.
Rosewill does NOT have a reputation for making quality PSUs - and the specs on that as seen here
indicate it is not one of their better supplies either - not with just > 72% efficiency.
So, what you need to do is swap in another PSU. This will confirm the problem noise is coming from the Rosewill PSU. It will also confirm if the sound from the speakers is caused by the PSU, and is not a problem with the speakers. Note too that noise from speakers can be caused by a number of things. One way to minimize is to ensure the speakers and your computer are at the same ground "potential" by ensuring they both are connected to the same wall outlet (facility ground). This of course, assumes the wall outlet is properly wired - which you can check with a good AC Outlet Tester
. I recommend one with a GFCI (ground fault circuit interrupt) Indicator as they can be used to test bathroom and kitchen outlets too. These testers can be found for your type and voltage outlet, foreign or domestic, at most home improvement stores, or even the electrical department at Walmart.