Glitches opening / closing Z flip 4

[art60folado]

Hi
I recently got myself another Z flip 4 from the used market. Everything seemed to be fine until I noticed that when flipping the device halfway, the screen flashes black for a split second. It doesn't happen every time, but sometimes you can even spot a line or two appearing horizontally in a random position across the screen. I feel a very small bump inside the hinge.
I will try to return the phone, but in the case the man doesn't respond anymore, I wanted to know if this is a known issue and if there is anything I can do about it.
Thanks in advance!

[BandOfBrothers]

Hi @art60folado 

Just as a troubleshooting step please try Clear Cache Files from the phone's System Partition Section  > https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/ You may need to insert your earphones or hook upto a powered On Laptop or use a Tv's USB Port to access the Clear Partition Section. This may help with lag or stutters as this clears the phone of old/unused or broken cache files.There is also a Repair Apps option in the Menu System too { Possibly excluding the s²⁴ Series of phone's } 

If you perform a forum search you should find existing threads with some further help within.  

However if this is a hardware issue then you'll need to know how old the phone is regarding warranty cover. 

In the UK Samsung phones typically have a 24 Month Manufacturer's Warranty. 

And Samsung may ask for the original invoice / receipt to arrange warranty work. 

If the phone shows any sign of an accident bump then they may charge a fee for warranty work. 

Personally I'd suggest to follow your current avenue of a return to the seller / merchant. 

If i can be of any further help please don't hesitate to ask  😎 

[art60folado]

Thank you for the help  
Clearing cache didn't fix the issue, so I will try to return it as said before.