OK, so after the 5th time going to the shop that installed my coils to get rid of rear squeaking, there is still squeaking, and I'm like
Chronological order of events:
1. coils installed along with all new OEM parts everywhere, not a single old part was used
2. after driving for the first time in the rain about 2 weeks after installing the coils, squeaking started in the rear after the car dried out
3. went back to the shop got them to regrease everything
4. squeaking was there as soon as I left the shop parking lot
5. went back in for regreasing
6. squeaking happened again as soon as I left the shop parking lot
7. went back in for regreasing and they reassembled the rear strut assemblies
8. zero squeaking noises anywhere until it rained again and the car dried out
9. went back two days ago to get them to regrease everything again
10. squeaking noise was there as soon as I left the parking lot
My conclusion is that, given that the only time when the noises subsided completely was when the rear strut assemblies were disassembled and reassembled, something inside the strut assemblies is making the noises, and every time it rains it just washes whatever grease was applied to wherever causing the very loud and noticeable squeaking noises.
I am out of ideas and about to get a second opinion from another shop cause this is insane.