PC freezes & sound loop

Hey guys,

my brand new tower pc freezes randomly while watching youtube videos or stream videos like movie4k. Sometimes 2-3 times a day, and sometimes only once. Everytime it freezes there is a soundloop of about 1/4 sec. and i have to shut it down. I already run memtest but it doesnt came up with any errors.
I also stresstested my pc, but it run perfectly.

Does anyone have any suggestions?

Here are some information about the pc and the system:

CPU: intel® Core™ i5-6500 CPU @ 3.20GHz × 4
Graphics: Intel® HD Graphics 530 (Skylake GT2)
OS type: 64-bit
OS: Ubuntu 16.04 LTS
Memory: 16GB DDR4 RAM
Disk: 500 GB SSD

Best regards,

attex