Hi all, been having a small problem with my crack as of late. It is a fuzzy crackling in the left channel only, it occurs on startup and then randomly afterwards. The volume of which is independent of the pot. One notable thing is that it occurs whenever I wiggle around the small tube in its socket. What do you think the problem could be, a solder joint, or RFI? I have heard of cleaning the tube pins but I am not certain on how to go about that. Any help is appreciated, thanks!