Dye UL's have always been very quiet for me. Another barrel I've found to be very quiet as well is the Inception Designs Stella barrels, the amount of porting on their one piece tips is pretty incredible.
I use Lurker as they are so lightweight compared to most other barrels except carbon fiber and almost as quiet. They also have the preferred longer bore like Stella. My one Deadly Wind CF barrel, seems even quieter though but I don't want to go the Freak route.
"Hokey religions and ancient weapons are no match for a good blaster at your side, kid."
I was pleasantly surprised by the eigen kit I just took in. Honestly it seems to vary from gun to gun .. The eigen was quieter on a G6R versus a PE FR/Pro tip, but it was louder than the PE combo on my CS1.
Was definitely odd. I was shooting indoor, too.
Regardless, I'm keeping the Eigen kit for myself but they're really nice for what they cost.