For what it’s worth, I’m noting the hiss/static issue I experienced with my BHK Pre below. Given the adjectives used above to describe these issues - thumping, pulsing, etc, tough to tell if it’s on point, but here it is anyway.
When I added the BHK Pre to my system switching out the previous preamp, I noticed a distinct level of hiss coming from both speakers that was not there with the previous component. Same level of hiss from both, present when music was playing or not, and at a constant level independent of volume. As Paul previously noted, there is some to be expected. Nonetheless, I thought the level to be a bit high, as I heard it from my listening position (10ft/3m). The hiss was present when both the stock tubes and the Tungsram 7DJ8s from Upscale Audio were in the system.
In addition to the general hiss level, there is a distinct graininess/pulsating static/hiss coming from the right speaker, fed by the (RED) XLR output. It is an odd pulsating static that emanates from all drivers on that particular speaker. Further testing confirmed the offending XLR output, as swamping the connections shifted the issue to the other speaker. Testing also revealed that hiss to be present without any other sources connected to the BHK Pre also.
Also possibly worth mentioning, although I am not sure it is relevant to the hiss problems. Using the BHK Pre in my system, I reached a comfortably loud volume level at setting of 30 (should have measured it with my SPL meter but did not). Given the theoretical range of 100, I found that notable. Not sure what others have experienced, as this is undoubtedly system dependent.
System note: IC cabling is balanced throughout (XLR); PSA DMP and DS DAC are the upstream components.
I’ve been working with the always excellent PSA customer service team to troubleshoot/resolve the issue, and had sent the unit back for a check-up.