Cat has started to growl while cleaning herself...not going into heat?

Three days ago my cat started to growl when she cleaned herself. It is similar to the growl she does when in heat (deep growl) and happens when she cleans her feet, back and sides. I checked out her and she has no sores, and doesn't react to pain in any way. She is still eating regularly with no problems or indications of a mouth problem and she doesn't growl every time she cleans herself either.

Has anyone else had this happen with their cat? She is not going back into heat (no other signs from her). She had been fed some tuna 2 days in a row and got sick, but that is the only thing that has changed... Also there's been a lot of stress in our house lately and I'm almost wondering if it's related.

Any thoughts would be really appreciated. We will take her to the vet if it continues a few more days or if any other symptoms appear.