Strange grunting sound

Question
Hi,
My female rat is almost two years old now, and I have made no changes in her diet but she seems to have gained a lot of weight. She also all of a sudden makes this teeth-grinding, grunting noise constantly (which she has never done before. and it's not a normal sound they usually make.) and I am just noticing that she is either coughing or sneezing frequently. I don't think her teeth are too long, and she eats food i give her, but she is acting more lethargic and seems uncomfortable.
Thank you so much.

Answer
 It may be that she has a respiratory infection, a tumor near or on her lungs, or that she is uncomfortable for some other reason.  Since she's a senior citizen now this is usually the time that tumors start to pop up.  Sometimes they are internal and cannot be detected from the outside.  I would take her to a vet for an exam and probably some antibiotics; perhaps clearing up her respiratory infection will make the sound stop.  Your vet will also be able to look into her mouth and see if anything is the matter in there.  Well I hope she feels better soon, good luck!