I've got a messed up screen that happens occasionally

Hi guys,
Recently my Nexus 9 would occasionally give me a messed up screen with around 3x10 mm white or other color blocks piled up the entire screen. And flashing.
Sometimes even with shocking noises like biiiiiizzzzzzzzzzzziibibibibibibibizzzzz

It would disappear if I use the power button + volume up combo to force reboot.
Sorry don't have a photo or snapshot yet. I'll try to take one if that happens again.

That did freaks me out when it happened the 1st time.
It just pops out from no where. I've tried to locate where's the cause or the problem but failed.

I just wonder if this is some sort of hardware failure? It does gets quite hot after the screen is on for a while.

Please if anyone ever had the same issue?
And please please please do tell me it's not something wrong with the hardware!

Thanks.

Cyanogen OS 12.1 occasionally crashing

So an issue I've had since moving from Oxygen to Cyanogen is that every now and again the system will lock up, and the only way to get it back is to press and hold the power button until it does a forced restart. Today it did it while I was paying for something using Android Pay and it asked me to enter my lock code. II drew my pattern and the system froze.

It's fine this before when using the camera, playing games, etc. It's pretty random.

I've also been having Bluetooth issues, but that's another story.