RGB fans fade randomly

[Nanaky]

Ok, so I've just put in a custom water cooling set up on my Rig. Which consists of a Asus Sabertooth 990fx r2.0 CPU is a Fx9590. Got 32gbs of Corsair Vengeance pro ram. Dual Sapphire rx 590's and a Corsair RM850X PSU. 

I'm using 5 Deep Cool RF120M fans. Everything seems to be running just fine and cool. But my LED's for the fans dim. Like at random times. My case is a Phanteks Eclipse P400S, which has a few RGB strips. Those also dim. None of my other LEDs dim. Same PSU. 

The only "new" thing I've added is the water cooling parts. Nothing is hooked up inline with the Cases RGB. I've torn down the whole set up three times now, and at a loss for words. Any help or comments would be appreciated. 

Btw computer boots and runs fine. Just the disco effect with the lights. 

[Semper]

Are your fans being curve controlled by Voltage by chance? I believe it's the case that LED's on voltage controlled fans will fluctuate with the RPM target that the curves are set to (higher RPM = brighter, lower = more dim)

[Nanaky]

The fans are on all the time, the LEDs kinda dim every 8 seconds or so. I've installed Fanspeed program to see if the RPMs dropped, but they don't. I think I'll just have to break out the old muti-meter and try to figure out what, if any voltage drops are happening.