The use of 都 gives the sentence an emphatic effect. (2) sounds more forceful than (1):
- 你的担忧, 我听见了。
- 你的担忧, 我都听见了。
都 is the trace of a series of operations as follows:
- The predicative relation "[我][听见][你的担忧]" ([X][V][Y]) is envisaged.
- A sense of alterity is introduced at the level of X, V or Y (in accordance with the context).
- The sense of alterity is then eliminated, which has the effect of "consolidating" the predicative relation.
When the sense of alterity concerns X, we could have something like:
Here, the sense of alterity comes from "You thought that I was excluded from 'having heard of the bad news', but actually I am no different from you all."
When the sense of alterity concerns V, we could have something like:
Here, the sense of alterity comes from "You thought that I didn't know it (没听见), but actually I knew it."
When the sense of alterity concerns Y, we could have something like:
- 你做的坏事, 我全都知道了。(全 is purposely added here to avoid ambiguities).
Here, the sense of alterity comes from "You thought that I only knew a small quantity, but actually I knew all."