Using contact cleaner in tube sockets

Thanks all for the input. I found a shop near me in New Haven CT that deals with ARC. I'm just going to take it in and have them take care of it. It will probable have to go to ARC. Thankfully the seller gave me a partial refund.

The best product hands down, first clean with 99% isopropyl alcohol
Craig make excellent small swabs. 
To protected long term over 10 years ,  and enhances tube socket conductivity 
As well as every thing  audio is  called Stabilant-22,   I have used many 
Many ,it is not messy has several applicators it comes with.
Check it out .it has been out for years even  NASA has been using it for years. 
Check it out.

Just a note the chances the bias will stay as set when shipped is slim as the vibration and knocking around during shipping will most likely change the bias a small amount so always better to do it locally with a reputable tech if the amp is not easily user biased. 

I chased a very similar noise for about a year on my tube pre-amp. Even replaced the tube sockets with gold plated versions. About $1,000 later it was ultimately a bad ground.  

Duder, did you switch tubes  switch channel's. 
 Is the cracking now comning from different 
Channel.  You should  Hope it is.