Research has shown that dolphin echolocation is so good that they can detect a 75 mm object at distances up to 100 m away.
The debate over dolphin language goes on and will until we can 'crack' the code. In the mean time there is mounting evidence that they do communicate ideas in a sophisticated way.
Scientists have shown that the same species of dolphin living in the English Channel stick to either the French or English side and never mix. Is it possible they stay apart because they don't speak the same language?
At the moment we believe they have vocabularies similar to apes complete with food sounds, danger sounds, and 'seeking' sounds. There are many more sounds that we don't understand at all.
Dolphins can assemble short strings of sounds the way we make sentences. We are also pretty sure that they use distinct sounds to represent themselves; they have a name and this is recognized by other dolphins.
Noise probably isn't a problem for dolphins in captivity but it is for wild dolphins. In Datai Bay where I work, I sometimes hear dolphin whistles but they are often drowned out by the sounds of trawlers and heavy ships passing.
Lots of ambient noise would be like trying to chat at a rock concert. This could make communication and echolocation pretty difficult. More about this in another post.