I am, I think that REAPERUK is on to something though, it may be what he was saying.
I went upstairs and discovered that my 2nd surge protector has a seperate earth light on it (Didn't realise), picked it up and bought it downstairs to plug it in since I remembered he said it could be an earthing issue, and low and behold, the earth light isn't on, it was on when plugged in upstairs. So it could be an earthing issue causing my crackling audio after-all, which means no matter what I plug my PC in to, whether it's an external DAC or sound card I'll always get the crackle. Not sure really where I can go from here regardless. But it's pretty funny that, that was probably the cause after all of this. I just assumed the light on my old surge protector was indicating surge and earth, which it wasn't.