ground loop with new interconnects?

I know this topic has been discussed, but I'm not finding anything that relates exactly to my issues.

I have a ARC D115mk2 amp, vandersteen 2ce and sub, Klyne pre and a Pro-ject RM 10 turntable.

I noticed a slight hum when I switched the interconnects on my TT -- from cheaper Audioquest astral blues to Klyne dragonflies. I just purchased Nordost red dawns (thinking the interconnects might be the issue) -- It did not solve the problem. The hum gets louder as I increase the volume.

This hum is decreased somewhat when I unplug the power to the sub.

I also switched out the inexpensive monster interconnects from the pre to the amp with another set of red dawns -- now I have a hum that starts after about a minute and is not effected by the volume control.

Questions:

1. why is the problem only heard with the better interconnects?

2. how can I solve this issue and keep the better sounding interconnects?

Thanks.