BHK Pre owner here (since late 2019)…
I found this thread while google-ing PS Audio BHK preamplifier whining. I too experienced this problem when I decided to replace the stock vaccum tubes after ~2500 hrs of use. Taking proper precautions, I replaced the Psvanes with pair of platinum grade Genalex 12AU7s from Upscale. I turned on the rear switch and after a minute pushed the front panel switch on and the whining started exactly as in Excelgam video. This whining was NOT audible through the signal path. I checked to make sure the tubes were seated properly and it was. I tried power cycling without success. Since the whine was annoying, I put the Pre on standby then turned it off leaving it powered off (not in standby) overnight. The next morning it turned on the back rocker switch then after a minute pushed on the front switch - no whine!! For 2 days, I left the Pre on play music to break in the tubes, no problems. So I put the Pre on standby mode. The following evening, I pushed on the front panel switch and the whine is back! Once again in put it on standby then turned it off completely. Next day I turned on the preamp and took it out of standby while it was still cold - no whine again! So it seems to occur when the Pre is warm. I used a fan to blow cool air on the Pre but that did not stop the whine either. The only solution was to power it off and allow things to cool down completely (I did not try different cool down times).
Finally, I decided to try a different set of tubes. I got a pair of SLN grade 12AU7C’s from (RAM Labs) tubeaudiostore.com. I replaced the Genalex with the 12AU7C, turned on the Pre and took it out of standby - no whine! Played music for a few hours and then left the Pre on standby when I was done. The next day when I took it out of standby mode there was no whine! It has been working normally for the past week.
I contacted support they kindly opened an RMA for me. Their hypothesis was it may be a bad regulator. Upscale did not think it was an issue with their 12AU7’s but I noted that the Genalex tubes had different construction than the stock Psvanes. They have single top insulating spacer vs the 12AU7C’s from RAM Labs which had two top insulating spacers like the original Psvanes.
I am trying to decide if I should send in the Pre for warranty repairs. What do you all think? I might try putting the Genalex’s back in to see if starts whining again.