ST 70 10kohm variables

[leadtower]

Hi All; I changed out the bias resistors in my ST 70 with Shannons board because I wanted to try these Tantalum resistors. I changed them on all four power tubes and adjusted the bias nicely. But on one of the 10K Variables; when I touch the screwdriver to the slotted adjustment screw there is a sound through the speakers like a crackling.. So I changed that for a new one thinking maybe it was bad and the new one still crackles when I touch it. The board biases up correctly but I am not sure what that noise means. It is pretty loud. The other side is silent and both sides play music well. The crackling sound is the only issue.
When I adjust the bias I have the ground lead of the meter tied to the chassis and the live lead touching the 10 ohm resistor. As soon as the tip of the screwdriver taps the adjusting screw it happens. Any ideas?
BTW; I installed all oil caps from Angela on the board. Nice sound; smooth as silk.
Thanks All.

[TomMcNally]

I'm thinking loose tube socket - and the mechanical tap of the screwdriver jolts it. Try a plastic/wooden "tool" and see if it still does it. Tube sockets seem to be real problems sometimes.