ARC Ref 3 bad tube?


I recently have developed a nasty sounding sporadic crackling sound in my system. It only happens once during each listening session. The crackling also comes out of both speakers in stereo. I have an ARC Ref 3 preamp and an Arc Ref 110 amp. I believe I have a bad tube but would like some opinions to make sure. I had my amp serviced in September 2009 by Arc so I don't think there is a problem there. The tubes in the amp have 1300 hours on them. The Ref 3 has 2500 hours on it. I replaced the four rear tubes at 850 hours with 6h30p-dr super tubes. The 6h30p tube under the 6550c power tube is orginal however. I replaced the 6550c tube in the preamp at 2200 hours. This is what I think is possibly wrong.
1.) The original 6h30p tube could be bad since it must get pretty hot from the 6550c tube above it.
2.) I noticed the 6550c tube has a strange looking white residue sticking to the inside of the glass. It almost looks like fine particles resembling styrofoam. That doesn't seem right to me.
I think it would be one of these two tubes since I get the bad crackling sound in stereo and not just one channel.

Thanks in advance for any advice.
tlg
It sounds like many a tube had been put in and pulled out. It may be time to either replace your tube sockets, or have someone retention them. If they're prone to falling out, it's time. I try and tell people when you are pulling tubes out of their sockets do not rock the tube back and fourth or you open up the tube sockets. Instead, pull straight out. In the Ref3 you don't have a lot of room and I believe you have little constant current source transistors near the tube sockets. I make sure the power supply is discharged and place one hand over the tube while I pull straight out with the other hand. That way your hand is stopping the tube's momentum and you don't slam the top of the tube into the metal barrier.
I think this is common for Ref 3. Great sound but bad design. I did everything you suggested. Not new at this. Sold the unit and moved on from tubes. But I'm sure one of the reasons for the Ref 5 was to solve the gravity problem.
In mine opinion a white residue at the top of the tube mean it is no longer vacuum anymore the getter wil be gone then,you should replace it, and be carefull put it in again so nothing will crack.