Word function and back translating '今天难得工作轻松些‘
Congratulations! You got the exact meaning of what the sentence wants to express.

At the very begining, 难得 means hard (难) to come by (得), e.g. 难得的机会 means a chance that is hard to acquire; 这场考试难得高分 means It is difficult to get a high score in this exam. Here, it is an adjective (or a verb), obviously.

Later, 难得 is used to modify a sentence. From my point of view, 今天难得工作轻松些 leaves out the subject 我(I), which should be [(我)今天(难得)工作轻松些] (难得 as an inserted component) / [今天]难得[(我)工作轻松些] (难得 as a sentence adverb). And it can be understood as Today is a rare day when I am easy with work. My opinion can be validated from the point that all the following senetences don't have a subject.

Besides, in the first sentence 上班族常常会有这样的精力, 精力 (spirit, energy) should be 经历 (experience) here. I guess it's a typo.

And it is more natural to say 这些情况往往与办公室噪音有关。 instead of 出现这些情况，往往与办公室噪音有关。