If you do not want iems and are willing to spend a bit more the Sennheiser hd-25ii offer excellent isolation for about $170-$200. Plus they are small and will easily fit inside a briefcase.

If you don't mind the idea of having something inside your ear (like an earplug) then I would suggest looking at iems as they will give you the most isolation. If you find that iems are too uncomfortable then there are many full size headphones worth considering. I would have to reccomend the...

I have the coiled version and so far I have not had any issues. Do you still have the warranty? If so, maybe it was a manufacturing mistake.