Greetings, I am Dr. Pat. I have worked with birds for many years. I will do my best to help you. I am sorry that no one has responded to your question. I will try to help.
As a guardian of two greys myself, I can tell you from personal as well as professional viewpoint that these birds are very sensitive. Any change from normal routine can result in abnormal or even self-destructive behavior.
Are the sounds she make associated with breathing? are they more like a baby bird needing attention? can you describe when thes noises are made?
Something may have happened which the caretaker was unaware. Was there a heat wave? What there a fall, crash or other trauma? And the cats may be good when you are home, but are you 100% nothing happened?
If she is accustomed to being with people and out of the cage, the change in circumstances may have been enough to cause a mental and physical problem.
The first thing to do is to make certain that nothing is physically wrong. She should have a health check by a competent, bird-experienced and understanding vet ASAP. I know this can be stressful and may add to the mental trauma, so it is a balancing act since you have just returned. If there are no outward signs of illness, you may be able to wait a few more days but this is an important step and should be done.
I worry that the sounds may indicate respiratory distress, infection, fume exposure or even excessive heat exposure.
If she is suffering from the mental trauma of your absense, it may take months for her to talk again. The vocal ability is assicated strongly with physical health, mental well-being, self-assurance and self esteem. All require time to heal.
Without a diagnosis, I cannot recommend any particular course of treatment, except good nursing care at home.
If you feel comfortable with it, examine the bird thoroughly, using gentle restraint via washcloth or hand towel: do not restrict the chest or hold around the body. Check the eyes, nostrils, mouth and beak if possible, having a good look in there for mucus, redness, masses or anything else unusual. Palpate the tummy for pain, fluid, lumps or anything else (eggs, if female or unknown). Check all the joints for swelling, pain, and mobility. The feathers should be parted to view the skin, muscles and skeleton below; this can be done using a q-tip with isopropyl alcohol or KY gel. Look for bruising, lacerations, injured feathers.
Your job is to keep the bird warm, safe, quiet, and confined; and to provide adequate hydration and calories.
Pet/feed store medications and home remedies are harmful, ineffective, immuno-suppressive, and make them much worse and may interfere with the veterinarian's diagnosis and treatment. Do not use them. Homeopathy and natureopathic techniques do not work in avians and can actually be very dangerous.
I know it is expensive, but you may not have many home options, because the first thing you need a vet for is to find out what is going on. Treatment is only as good as the diagnosis. If you call around, you may find a vet to work within your means.
Toxins, infections, trauma must be ruled out and/or treatment begun. I really must stress that you need a bird-experienced person, and not just a vet who advertises that they care for birds.
You need to take your bird to see an avian-experienced veterinarian ASAP for complete examination, diagnosis and appropriate treatment. Check http://www.theparrotsocietyuk.org/index.php/Avian_Vets/28http://www.avianveterinaryservices.co.uk/http://www.birdvet.co.uk/ http://alanjonesbirdvet.yolasite.com
www.riversideanimalcentre.orgask if they really have worked with birds a lot. Unfortunately, this list does not rate competency or experience, but is only a starting place; the vets at least take the avian medicine journal and hopefully see a bird or two a year. The best referrals are word-of-mouth, so check with several non-bird vets, the humane society, parrot rescue groups, bird clubs, etc. for their input. As you might guess there may be controversy and varying opinions even with this. Even board-certified avian specialists may not have a lot of practical bird experience. Unfortunately there are few resources available to refer you to really good, clinically-experienced bird vets.
If this were my patient, and money no object, I would start with complete fecal analysis and direct smear, stained with Sedi-stain and unstained for multiple parasites, fungi, spirals; direct smear stained with Sedi-stain and unstained of the oral cavity; bacterial culture and sensitivity of the feces and choana. Depending on the case I might do a fungal culture. Routine blood work is necessary to rule out other issues. There are MANY DNA/RNA tests for bird diseases. Ultrasound is often more informative than radiographs and does not require anesthesia (ask your vet about this option). Generally I start them out on medications as indicated by the tests.
Your bird may need injectable fluids, calcium, antibiotics and many other medications. Act quickly and good luck.