I too had a similar hum problem when I switched out my Rega RP6 with my new VPI Scout ( 2016 ), using the Phoenix PSU Roadrunner Tachometer. After trying to isolate the hum problem and various scenarios for eliminating the ground loop I had no success. I did find the culprit however, it was the wall wart power supply to the PSU. I removed it from the system and the hum went away-dead quiet. I made the difficult decision of selling it, I opted for the quiet! The last readings I was getting from the PSU / Tachometer set up was a pretty steady 33.333. So I'm assuming the Scout is spot on. I hear no pitch derivations and every recording I play sounds just like I always heard it. I hope this helps. I'm not suggesting you do the same but I can say that I just enjoy the music now and I'm not obsessed with micro speed variances that I will never hear.