Yeah, that's not quite what I meant when I suggested parrots. What i meant is, if you teach a parrot to say "Hello", and then it says "Hello" within earshot of the affected subject, the test subject will then be able to perceive the word "Hello" (as long as you say it like the parrot did, "hellOOOOOO" — it's like the difference between the word "chirp" and an actual chirp).
Teach the parrot a few simple phrases - "come here", "eat this", "good girl". If the parrot can then be coaxed into speaking those phrases in front of the subject; from that point on, the subject's brain will consider those to be "bird noises" — and thus, when the subject hears those phrases, they will not be anomalously replaced with bird noises.
Of course, since all non-bird noises are being replaced with bird noises, that might reduce the extent to which this method is useful for communication…
(unless we bring in SCP-1849, of course)