[Windows Central Question]

Hi,
I had plugged my phone with a 3.5mm jack of a external laptop speaker and ever since the screen of my Lumia 730 started to flicke. It flickers a bit 4-8 times a day.
I hard reset the phone but no resolution.
Also one problem from start, ever since m purchase is that when i select open any email from the notification center and delete it i see round circular pixel sort of stuff on my screen before it comes to windows screen.
Screen flicker is troubling me, don't want my phone to be unscrewed only 2 months old. please suggest.