"Noble" is a broad word. One of Merriam-Webster's definitions describes it as "superiority of mind or character or of ideals or morals". And of course it is the subjectivity of that definition that is at the center of this debate.
First, I'll talk about heroes; you might want to skip this paragraph. A study of American veterans was interpreted. The assertion of the of the article I read, was that "heroes don't recognize heroism. They don't recognize it at any point, and they don't talk about it. The article expanded on that talking about the perceived motivations for heroic acts, and the demographical data on heroes. It said that heroes were more likely to be draftees, and that heroes acted out of responsibility. As has been said above, the military teaches you that the team is the beginning and the end of success and survival. The battlefield doesn't need any help confirming this.
Now heroism is easy. The proof is in the pudding. Now Iraq is a good example, because it's got a little of everything. For Operation Iraqi Freedom, the US military has about 300,000 direct employees on the ground, but only 75,000 are combat troops, and there is no defined "front line", there are tens of thousands of miscellaneous contractors involved in the war effort, and tens of thousands of private military contractors. In the Iraqi invasion of Kuwait, there was a front line, and honor kind of sorted itself out. There was a clear aggressor, and a victim. So we have aggressor soldiers, victim soldiers. In OIF we have ambiguous soldiers, soldiers for hire, stagehands, stagehands for hire, and the group of people hosting the party, insurgents, guerrillas, religious militias, certainly over in Afghanistan drug foot soldiers, and anybody I'm leaving out.
Now, ignoring "if soldiers are noble, which of those groups are noble soldiers?", let's look at the famous quotation, "War is not merely a political act but a real political instrument, a continuation of political intercourse, a carrying out of the same by other means." In Iraq & Afghanistan, the US, and the Maliki Government are using the instrument of war to combat tribal power, drug trafficking, religious strife, post invasion insurgency, alleged state sponsored terrorism, and wide scale foreign terrorism. This seems to be a commingling of all American military fiascoes of the 20th century; American interventions in South-East Asia, South America, the Middle East, Africa, and Eastern Europe.
So we've got bungling foreign policy leading American Civil Servants, in jobs that are the most dangerous, the least rewarded, and at times, the linchpin of our national security, to places where they should, or shouldn't be, so they can get shot at. In several cases, America lends it's military as a proxy military to other governments. In Vietnam the problem with this, was that at times, the government using Americas military in proxy, was villainous.
The problem I see with the supposed inherent nobility of the sacrifice of soldiers is that it boils down, as I see it, to sacrifice for a good cause. When the cause is good, the soldiers are noble. I think much of the confusion is not the nobility, which is a nationalistic red herring, but both the respect for the selfless civil service of military service, and being part of the class of citizen that is entrusted with the double edged sword of the power of killing, and the risk of death in national service to potentially protect the nation, or otherwise honorably distinguish themselves (by fighting fascism, or by participating in disaster relief).
Implicit in the role of soldier, is following commands. The nobility of commands is what distinguishes a noble WWII veteran from any thug following orders. Perhaps an example better then a peacetime soldier, or a soldier in Iraq, is an Israeli soldier. Is it a war on terror? Which side is which? It's a segregated society, and even with Israel's Democratic ideals, and system of Justice, their honor from a third person point of view is ambiguous. Are their foot soldiers any more honorable then those of an Arab kid who joins some "terrorist" group because of his experiences of being on the receiving end of Israel's poorly restrained warfare, or their divided society.
Back to WWII. Hiroshima, Nagasaki, and firebombing. It was a complicated situation, but you don't drop the bomb because it's the right thing to do. You drop the bomb because you have to. In one plane, it was honorable. In the other it was a day that will live forever in infamy. The telling thing, is that that is about the most concrete example you'll get, and what's concrete about is it, is that you know that it's both honor, and dishonor. Soldiering would be honorable if it were not for the warfare.