The voices echoing off the walls are so annoying in this room.
Literal
Talking-voices [subject-が] wall [against-に] echo [and-て] noisy [emphasis-な], this room.
Sentence-final この部屋 is a right-dislocation — the topic stated after the comment as an afterthought. Very natural in spontaneous speech: the speaker blurts out the complaint first, then specifies where. The な is the musing/emphatic particle (not the prohibitive), softening the complaint into a grumble.