Question edited for clarity, added a few Capital letters and 'light' instead of the American spelling of something that is not 'full fat' or 'full featured', or in other words 'lite'..
Remove the plates and the light and reinstall them, making sure they are fully locked home. Some buzzing is normal as the electricity generates the negative ions and the electrostatically charged plates attract dust , pollens and allergens.
I believe the beep when you initially plug it in is normal. I don't think this model requires replacement filters and if not, the beep is not related to a sign the filter needs replacement.
I also think that the buttons on the side reflect two different speeds at which the device may be set. I am unable to find a manual for this model. You may try to contact the manufacturer: https://the3q.com/pages/Contact-Us.html