Issue now resolved, turned out to be a faulty case cable. Thank you for all your help
Any chance you could elaborate on what cable you mean? (Power cable to PSU, Sata cable to HDD etc...)
I've been suffering with DPC Latency for ages but it has reached an all time high now where I get audio crackles all the time and even my USB devices (mouse and keyboard) intermittently disconnecting/dropping out.
Thanks.