Heya Ctag! I have been reading through your thread and its really cool to see someone who is keeping their civic alive!
Uhoh... The rear brakes are starting to "shush shush shush" again. $10 says they'll go back to how they were. What could be causing that?!
Im a former Honda technician, and I might have a few ideas to help you with your brake pulsation. Brake pulsation can come from a few different things, but two are the most common. Either the rotors/drums have hot spots, or they have excessive runout.
Hot spots are caused by heavy braking. You can see them as slightly discolored (darker) areas on the surface of the rotor/drum. You can google "brake rotor hot spots" to see pictures of what I'm talking about.
I know you probably don't feel like you do heavy braking, but in reality these civics came with very small brakes and coming down from highway speed means that there really isn't a lot of surface area for the rotors/drums to dissipate heat. The only real way to get around creating hot spots is to upgrade the brakes with either larger ones (perhaps replace the front brakes with ones off of an integra?) or to get rotors that are drilled and slotted (so they have more surface area, and can dissipate heat easier). I would warn against drilled and slotted rotors on a daily driven car, because if they start to have problems with squeaking or vibration, you can't resurface them and you have to replace them.
Excessive runout can be two things. Either its high spots and low spots on the surface of the rotor/drum, or the rotor and drum are not seating properly.
Here is what I would do:
I have seen A LOT of brand new drums that are out of round. Especially when they are inexpensive replacements. I would suggest taking the drums to a tire/brake shop and having them resurface the drums using a brake lathe. That will ensure that you have a perfectly round surface for your brake shoes to run against. A "shush shush shush" noise is usually caused by the brake shoes slightly touching the drum in a certain spot. The other thing you can check is to make sure that the backing plate isn't touching the drum at a certain point. Also, I don't know if you have adjusted the rear brake shoes, but if you do, then I would recommend using a couple of lug nuts to keep the Drum fixed securely against the hub (so its not slightly crooked).
That brings up the second thing that I would try. I would make sure that front and rear hubs are REALLY CLEAN from any surface rust. You can imagine that even if there is 0.01 of an inch of rust on a certain spot on the hub, that it would be multiplied 10x by the time you get to the outer edge of the rotor. You can use a wire brush and a flat headed screwdriver to scrape off all surface rust from the hub when you install the rotors and drums.
Its much less common to see new front rotors that come out of the box with excessive runout, so If you replace / resurface the front rotors and make sure that the hub and rotor surfaces are clean from rust, then that should really help you avoid brake pulsation.
Of course, all of this information is assuming that your wheel bearings don't have excessive play (extremely rare on these Hondas) and that you don't have bad suspension parts (upper ball joints, lower ball joints, outer and inner tie rods, etc).
I know this is a lot of information, but I also hate brake pulsation/noises and I would love to help you fix your civic and keep it on the road! Let me know if you have any questions.