I'm new to tube preamps. Please help. There are 5 tubes in this preamp. I can hear a buzz/crackle sound through my cabinet along with hiss and when I lightly knock on the rack a pinging sound comes through. Which one (s) are making the noises ? Can I just switch them around ? I don't want to call the company - there cool enough people. I'd like to learn so I'm asking you. I've already diligently written down each tube's labeling. At this point the amp's tone is mid heavy for me - I need a deep, dark and clean tone. What can I do ? From the image from the lower left corner moving counter clockwise it has: 1) 7025/12ax7WA Sovtek 0505(month and year?) 2) same as above but with 0506 3) 12 AU7A / ECC82 EH 0404 4) same as 3) but with 0503 5) same as 3) but with 0404 Please help. I know you know way more about this than I do.