Good small/single outlet power conditioner for preamp.

have you asked the equip makers/dealers for help/ideas?

@elliottbnewcombjr yes, the Preamp maker has been very helpful, guiding me through lots of these checks. 

I would continue to troubleshoot until you are certain of the problem, then solve that. It will be very interesting to see if the problem goes away when using a power strip only.

Update: The Furutech tp-609 passive power distribution unit AND the Equi=Core 1800 balanced power conditioner are BOTH hum free!!

This confirms some sort of mismatch in power or grounding between the Puritan PSM156 and the Backert Labs Rhythm 1.4 preamp. 
 

So if I elect to keep the preamp, I will need to invest in another power conditioner for the main system here… maybe a new thread for that… Unless anyone has a good recommendation for something at least relatively close to the $2300 price of the Puritan, but some more $$ is fine to consider. The Puritan is so good at its price, I’m worried what it’ll take to match its performance. 

There are many excellent power conditioners on the market.  Furman is only one of many and Erik_Squires recommends this brand mostly because he owns one and likes what it does.  I use Shunyata and many others use other brands.  There is an Audioquest Niagara 1200 available used here for around $700-800.00 which is an excellent value as well.