Tube amp crackle noise with pre-amp volume at zero.

yes bti red led will light up on the power tubes if one operates outside of what the primaluna amp bias range allows

coughing tubes usually small signal tubes... try fresh set, or move tubes side to side to isolate

primaluna supplies sino shuguang tubes labelled primaluna... primaluna gets them with more quality control but the qc is far from perfect, and the modern tubes often wear out get noisy faster than old stock ones due to poor materials poor manufacturing of the tubes 

Thanks for the reply's.  I'll try cleaning the tubes and see what happens.  Next time I'll look for the red indicating lights.  In the end, lesson learned on audio tube suppliers!  Thanks for the leads guys, very helpful.

Many tubes have a small amount of gas or material inside, forget what they call it but its to facilitate electron transfer. This material can condense in different places when the tube is cold. Then as the tube warms up as the little bits turn back into gas or fly off in little pieces they of course go from electrode to anode and upon hitting the anode create a little voltage surge which we hear as a pop or click or static. 

Eventually this all settles down. Usually. We hope. Welcome to the wonderful world of valve amplification.

Gold Lion KT88's

Tried em, return them, 
Went with Sve 6550,  nicee upgrade over GL. read  somewhere  on the INet another audiophile same reaction,,but hey, maybe your system is dif, 
,,back to OP, yes 1 power tube is going bad. 
Sve's 6550's built like tanks to last. 
These are musical power tubes.