HP laptop screen flicker

My HP Pavilion Model 15-cs3063cl screen started to flicker recently. I disconnected the power and held down the start button for 60 seconds before restarting which worked temporarily, but the problem recurred the next time I booted up. What would you suggest? (FYI – previous to this, the PC would “buzz” when I start it up and then randomly. I’ve cleaned the cooling vents and make sure BIOS was up to date and still have the noise. I recently updated to Windows 11 – This had no effect.)