Did you get an unbeatable deal on the 50SE that can't be passed up? If not, here's what I'd say. Unlike the others my thought is, you just took delivery on a used preamp and you're immediately having a problem with a "loud" pop. You should contact the designer to see what he says. The seller was fair enough to say you can send it back if you're not happy. I would take him up on that offer after I hear from Victor unless the problem can be resolved without shipping the preamp. . At this point are you happy? Plenty of BAT preamps show up here regularly including the 50SE. You can get yourself another and not have to deal with an issue right out of the box. I sure wouldn't want to have to be hearing loud pops, posting for help, emailing the designer, facing the possiblity of having to ship the preamp for retubing, and trying to troubleshoot on a preamp I just bought. Now if it just needs a re-tube and the designer says, "sounds like tubes" and you don't mind having to ship the preamp, and wait for it, then ok. Me, I woudn't be shipping a preamp I just took delivery on unless it was back to the seller. Now, if the tubes were exposed and a simple process to get replacements and re-tube, that would be a bit of a different story. If your popping problem is tubes and you can do the re-tube yourself with BAT supplied tubes fairly simply that would be a different story too. But at minimum it sounds like you face shipping the preamp to BAT, unacceptable.