Mine also do the same thing. I did have a problem about 2 years ago with my chihuahua. She was throwing up a little blood and passing blood. Couldn't figure out what the problem was. After 2 vets saw her in our local area and couldn't find a thing wrong with her, I took her to my old vet 6 hours away! After several test and x-rays he finally said it was due to eating sunflower seeds or hulls. They were scratching her insides and causing the bleeding. I kept her away from the cages, vacuumed 10 times a day and all is well. Oh yeah, it cost me over $1400.00 to find out what the problem was. I'm sure it could have been serious if we didn't find out what it was, and if she kept eating them.
AND, only one of our birds gets sunflower seeds. He is a grey that will not switch over completely from them, although he is getting less every day and more fresh veggies like the others.