I just read the title this morning and realized your Crack has crackling sound. Sounds like it could be normal??? (Tongue-in-cheek!)
Aside, Paully is visiting this weekend. He is still sleeping, but I'm an early riser, and I can't change that by much on the weekends.
But seriously... I don't know what was in the old thread to help with crackling. So here goes:
First pull and reseat the tubes 6 times each. More if you think it might help. This cleans the tube pins and the socket. Even though they are both new they have been around since manufacture and might have some oxide on them.
Since flexing the chassis, moving the circuit, makes some difference, the next try should be the chop stick check. I often use a Pentel roller ball pen. But stole a chop stick the last time I was at a Chinese restaurant. I can use them, I chose not to.
This test is to listen while the Crack is upside down. Use the insulated item to push on each and every solder joint. It doesn't have to be a ground, it could be in the signal path, or power supply.
If it is a (dreaded) "COLD SOLDER JOINT" you will hear it cutting in and out as you flex the solder joint. You don't have to push hard, the fact that it crackles all by itself says the joint should be loose.
Yes, this takes a while but it is worth the effort.