I have an intermittent problem with my Fender Bassman 350w combo. Normally, I have no problems playing at a "normal" volume -- volume 7-8, gain at 3-4. If a dig in too much and send it into overdrive the signal starts to crackle loudly. If I back down my playing and even the gain or volume it still crackles and doesn't return to the quiet it was before. Last night the crackle was so loud, I had to turn the amp off for a moment, then turn it back on to clear the noise. If I turn the amp on its side, or upside down the problem goes away completely and I can crank it as high as I would like without any crackle or other noise. Flip it rightside up again and the crackle/noise comes back. If I play the next day, there is usually no crackle right side up. I have had the amp for about 6 months and this is the second time this scenario has played out. The first was about 3 months ago with no problems in between incidents. My theory is that there is a problem with the jack but before I opened it up, I wanted to get others' opinions. Then, again it could be with the pre-amp so I don't know at this point. Other than this glitch I like the amp just fine. Thanks in advance for helping me troubleshoot this.