so they are shoulder mounted. does that mean i can fire them in addition to my other weapons?

why aren't they "Pistol"? I can't use them in melee - that seems a bit strange. standing right in front of an amplifier makes you immune to the sound waves?

what are the traditional noise marine weapons? all the noise weapons are ranged. are there any melee weapons? maybe from the boardgame?

oh and can you carry/use both, a blast master and a sonic blaster at the same time? or can you even dual wield them as long as you don't fire them on full auto?

On the topic of firing them with others... possibly. You can certainly carry another weapon, since as the text mentions, your arms are free, and thus decide which to fire on your turn with no need to draw and holster etc.

Firing both at once, however, is somewhat of a gray area. If you have two-weapon wielder (ballistic) talent, the text on page 244 says you may fire two ranged weapons that are either pistols or could reasonably be fired one handed. I, personally, would say a doom siren and another weapon would easily fall into this category, but it is something the players and the gm will have to reach their own position on, depending on how "semantic" they feel like getting about the strange provision that requires them to be capable of being fired one handed.

For extra fun, the text under page 147 says you may fire any basic weapon one-handed at a -20 penalty, and thus may ALL be dual wielded, albeit no in melee.

As for firing it in close combat. No, you may not. In terms of rules, there is no leeway here. However, I'd say this makes a certain amount of sense too. Aiming with something strapped to your shoulders, especially something with no articulation for aiming (it is a spray weapon, it does not require nor come with accuracy) is hard. Aiming at something less than a meter away, fully capable of dodging down to let the stream of killer sound pass over them is harder. Because it's a focused cone of sound, so a few inches can make the difference between being completely safe and vibrated into giblets. Whether this makes scientific sense I'll leave to the more scientifically minded, but within it's own internal logic, there's reason to be had.

As for the blast master, yes, you can carry both at once. Your gm might claim your armor doesn't have enough juice to power both, but that's a separate issue, easily resolved by taking the infinite energy upgrade available to all. As for the topic of firing both at once... see above, with the added complication that the Blast Master, as a heavy weapon, might make your GM look at you funny due to fear of you min-maxing a bit.

However, I have to point out: Neither HAVE full auto as a firing mode, and the actual two-weapon wielder rules lets you fire all weapons you're wielding on any rate of fire. So a guy with two knives can make two separate lightning attacks, a guy with two autopistols can full auto with both etc. This can get really messy when combined with multiple arms. However a lot of people are leery of this particular facet around here, me included, for what it's worth.

thanks for the answer.

the sonic blaster has full auto (s/2/4) but counts as heavy weapon when fired on full auto.

as it stands right now, my noise marine has a WS of 27... tactic is to dodge everything, disengage with acrobatics and blast them for a far.

oh and i have another question.

I know that the malus for running (-20 to BS for targeting a running enemy) counts for the whole round, until you act again.

IF the siren would have the sopophoric musk demonic bonus, every creature not dedicated to slaanesh would suffer -20 Perception and -20 Agility tests in a 2m radius. someone attacks me, suffers the penalties. I disengage with acrobatics and shoot. would he still suffer the penalties until my next round begins?

Ah. With the previous topic in mind, I figured you were talking of combining a blast master and Doom siren. In this case, yes, technically you can dual wield both. However, once again, whether your gm considers this a feature or a bug is something you need to discuss prior to you trying to pull it.

Probably not. Things that last longer in strange ways, such as the running penalty, tend to point out that they last in that way. For the musk, it affects all within it's range. Once out of range, they stop being affected in my book. Same way a character who moves out of a smoke screen no longer takes the penalties/bonuses for being in it, as soon as he's out of it.