RCA interconnects are suppose to be 50ohm, video and digital cables are 75ohm.
Try lifting the cables off the floor on paper cups, and even consider spraying some antistatic spray on the cables and floor especially if you are running your heater and have carpet.
Move the preamp close and try a short interconnect to see if the cable is the issue causing the hiss.. This might be painful but just get some cheap speaker cable (16gauge ratshack or something) so you only have to move the amp near the preamp.
If you are running a tube phono, swap those tubes out or swap them left-right if one side is doing it more than the other. This way you can check to see which tubes you are having issues.
Try lifting the cables off the floor on paper cups, and even consider spraying some antistatic spray on the cables and floor especially if you are running your heater and have carpet.
Move the preamp close and try a short interconnect to see if the cable is the issue causing the hiss.. This might be painful but just get some cheap speaker cable (16gauge ratshack or something) so you only have to move the amp near the preamp.
If you are running a tube phono, swap those tubes out or swap them left-right if one side is doing it more than the other. This way you can check to see which tubes you are having issues.