Random system freezing - Ubuntu 18.04

I am running Ubuntu 18.04 and I am experiencing often and random system freezing.
This is happened to me with a fresh Ubuntu 18.04 installed on a SSD.
The same freezing problem has previously happened to me with Ubuntu 17.10 in dual boot with Windows 7 on a HDD.
99% of the time when the freeze occurs my audio glitches for a couple of seconds together with the freeze.
The audio stops (music, movies, youtube, etc) and the system remains frozen.

My machine:

Graphics card:
AMD Radeon HD 7790

Processor:
AMD FX-6300 3.5GHz

Motherboard
MSI 970A-G43

Steps I took after some research:
- Installed UKUU and switched to a newer kernel.
I tried this several times with different kernels.
Problem persisted.

- Installed Mesa drivers for Ubuntu.
Problem persisted.

- Installed AMD drivers for Ubuntu.
Problem persisted.

This maybe related, or is a separate problem.
I am experiencing long boot times, and on every boot I get the message:
failed to connect to lvmetad falling back to device scanning

Often, but not that often, my system will not boot at all, and is stuck on the Ubuntu splash screen.
Some times on the second (2) dot, sometimes on the forth (4).

- I've tried editing my grub file to:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash amdgpu.dc=0"
Problem with long boot time and freezing persisted.

In the logs, the first logged event I have is:
Hardware:
radeon 0000:01:00.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0x7448

I believe the problem to be related to my graphics card and/or graphics drivers, however, the same graphics card behaves normally on the Windows 7 OS. This should imply that the problem (if related to the GPU) should be with the drivers rather then in GPU hardware itself.

Please tell me if any more information is needed on my part, as to precisely identify my problem and how to fix it.