I can THOROUGHLY recommend the one Wile and I have mate. Phresh Hyperfan Stealth / Silenced. Expensive but ridiculously quiet. I am freakishly weird about noise in my room and literally, a mouse farting is louder. I cannot hear mine unless I go right up to it and even then I can only just hear it even if nothing else is running! Spooky. I was struggling to believe the reports but it really is a dream.
Also have tried stringing two tents together in series and it worked fine. No splitter, just passive into both, and then a connection from one tent (which now works as a huge passive intake basically!) and the other (where the fan and filter were). Both tents get fresh air from passive intakes, and both tents get scrubbed through filter and replenished plenty of times per minute/hour whatever.