Just picked up a used Eden WT550, love the tone. While sitting idle with the the gain and master set and my passive bass turned down it lets off the occasional pop and crackle. I have, changes the tube for a new one, cleaned all the inputs jacks with Deoxit, opened it up and tapped (using a wooden chop stick ALWAYS USE WOOD FOR THIS) all internal parts/connections and nothing seemed loose, finally just eyeballed anything burnt or blow and could see anything out of place. I'm wondering if anyone has experienced this issue and offer any knowledge. There is also a pop when the thermostat controlled fan kick in, is that normal?