We have been to two different vets and put our Siamese cat, 10 years old, through two courses of antibiotics/ rhinitis treatments plus injections. It doesn't seem to help, she snores and snuffles, not all the time but it sounds bad when she starts. She is still active and affectionate, eats well and doesn't seem to have any other problems. She had a blood test for parasites.

Should I just leave it be? Both vets gave up.

Googling it didn't help much.

Leave it be and let the cat enjoy its old age.

While you could try a university veterinary hospital, I tend to agree with the above. If the cat seems happy and healthy - -and especially when it is an older pet -- and since the vets have presumably ruled out serious cardiac or respiratory disease, often best to leave it be. The potential treatments and investigations may do more harm than good.

P.S. Don't know if this is the sound you mean but you may enjoy this video

Leave it be and let the cat enjoy its old age.

You were right, she just died very peacefully, only seemed to be unhappy this morning. Good advice.