Firstly - Assuming that noise is indeed the problem then I would agree with the earplugs recommendation but it feels a bit weird - and the noise of the plugs themselves - expanding or moving slightly in your ears - can even be a problem if you are very affected by noise.
I used to be very sensitive to noise and got very frustrated with a flatmate once when I was trying to study in the evenings for professional exams (and he wanted to watch TV at full volume in a neighbouring room).
Then a friend , who'd grown up in a large family with noisy younger siblings around, told me that it is possible to train yourself to switch off from external noises and to focus. I didn't really believe it - but it does work - it just takes practice. You have to kind of 'go somewhere' in your head and after a while you can train your brain to switch off to external distractions. This works well for most types of work but it's not always easy at the start.
It is similar to meditation techniques in a way - and I found that meditation incidentally also makes you good at suppressing noise distractions when in a non-meditative mode - so it must use a similar part of the brain and it is definitely trainable in my experience. Sometimes now I don't even hear the doorbell when I am working at home - if I am in noise suppression mode.
Secondly, is it really noise that is the problem? I noticed that I am easily distracted by noise (or anything) if my mind is just in a distractable state.
So the cause appears to be noise but it can be that this is just a symptom.
The real cause being that your mind is irritable about something else - and then anything will distract you.
You might need to figure out what is niggling at you that is making it hard to concentrate - albeit that the noise is not helping.
The worst scenario is when the problem that is actually bothering you is the work that you've got hanging over you ! i.e. worrying about how much you have to finish etc This then turns into a bit of a self propelling problem - you worry and are easily distracted...the distraction delays you ...and then you worry more. Not good.
Hopefully you don't have that situation.
To drown out noise, and get 'into the zone' , I would also vote for certain classical music on closed in type headphones (something without too much change in tempo or volume)
I also regularly resort to using one of the meeting rooms or boardrooms at my office when my normal office becomes too noisy and I have an urgent project to finish. Sometimes I also have to put a note on the outside of the meeting room door to emphasize the 'do not disturb' plan and also tell staff on reception and secretaries not to put calls through.
I have had staff come and find me in the 'quiet room' even after all that though - so you have my absolute sympathies for your search for peace and quiet.