The pot noise could be as simple as a dirty or bad pot. Or, there could be DC on the pot. Check with your meter to see if there is DC there.
On the hum, since you've already changed electrolytics and tubes, start on one end or the other and remove tubes to see if you can isolate the hum to a particular stage. In other words, pull V1. Still have hum? Pull V2. Still have hum? Etc.