There are a few mentions of music in the 40k universe (Mostly in some of Abnett's side-story books interestingly) and generally they are keeping with what you would imagine in anything related to 40k. The general 'Imperium' kind of music is operas and classical symposiums, very late-Renaissance/Early WW1 style music. They're even played on old record-players like what you think about particularly old music.
There is also mentions of things such as 'Beat' (I believe it's called, it has a name similar to that. Thump maybe?) that is more like club music, as well as mentions of rock and such. It is very specific to the culture and to how 'liberal' they are. If you know anything about 40k, they take a very dim view on anything liberal, but it exists, usually as an underground sort of thing.
As far as Emperor's Children and the Noise Marines go - if you want to qualify that as music, think about the most gnarly, hardcore, screamiest discordant black metal you can find on youtube (Gotta love Noise Marines). GEnerally, though, they would prefer to just listen to completely discordant, chaotic noise.