This does sound like a power problem of sorts, this is not limited to the battery or the AC power adaptor and another component such as the inverter for example could be on the way out.
One thing I did discover just a few minutes ago was that when I unplugged the power cord and ran off of battery power the flickering stopped.
What happens if you remove the battery and use the notebook when connected only to the mains power by way of the AC adaptor.
I always run this laptop connected to AC as it is the main family computer. Also, I noticed when I unplugged the power cord that the battery indicator was only at 56%. Shouldn't it always be at 100% if it stays plugged in?
If you use a notebook over a period of time with both the AC adaptor connected and the battery in place the latter will be damaged and reach it`s end of life expectancy prematurely, the solution to this under normal circumstances would be to fully charge the notebooks battery to 100%, remove the battery and store it somewhere safe, once in a while remove the AC adaptor, replace the battery then use the notebook until the battery runs out of charge, connect the AC adaptor, fully charge the battery, remove the battery and repeat the cycle when the time comes, this is basically exercising the battery and so will keep it fitter for longer.
Just a FYI, most if not all notebook main batteries have memory chips and if you constantly use a notebook with both the battery and mains power attached the battery becomes reliant on being told it is 100% charged by it`s memory chip and if the memory chip is damaged in any way it can prevent the battery from charging up to 100% and in some cases charging in any way at all, some batteries have a simple reset that can sometimes help and you can find some information on that Here