I'm trying to fix an issue that my girlfriend is having with her kitchen sink. when the water is turned on, whether it be hot or cold, it makes a whining/squeaking sound. I've shut off the hot and ran the cold by itself and vice versa and it still does it, I've also removed the aerator, still does it whether its on or off. i have replaced the seals in the stem and still the noise remains. is my next step to replace the seat washers in both handles,replace hoses, or just replace the faucet altogether?

Here is what i know for sure about the faucet: 1. it was installed almost 6 years ago, and has made the sound since it was installed
2. it does not have an official brand stamp anywhere on it or the hoses ( so no company to troubleshoot with )
3. it was ordered via internet ( dont know where from )