After shutting down or putting the computer to sleep, the fans continue to spin for a long time (4-7 minutes) before turning off. In the case of sleeping, the power light on my case begins to flash at the same time that the fans power down. Note, this is not the same issue as those who have reported their fans continue to spin indefinitely.
Incidentally, my machine also takes a very long time to awake from sleep (4-5 minutes) or sometimes fails and simply resets or restarts. The problem existed before modifying the CPU voltage and is not affected by switching the RAM between auto and XMP.
OS: Win 10 Pro 64-bit
Mainboard: ASUS Z170 Pro Gaming
CPU: Intel i7 6700 (6th gen), Stock HSF, Undervolt Offset -0.15 V, LLC 4
RAM: Corsair 2x8GB DDR4-3000
Graphics: Gigabyte NVIDIA GeForce GTX 950
Sys Drive: Samsung Evo 750 SSD, 250 GB
Data Drives: OCZ Vertex 2 SSD, 60 GB; WDC WD1002FAEX-00Y9A0, ~1 TB; WDC WD2003FZEX-00Z4SA0, ~2 TB; WDC WD2002FAEX-00MJRA0, ~2 TB; RAID 0, ~300 GB [Maxtor 6B160MO x 2]
PSU: XFX TS 750W (P1-750S-NLB9)
Bluetooth: Parani UD100 Bluetooth USB Adapter
Monitor: LG 21.5" W2246S-BF 16:9 Wide LCD Monitor 1920x1080 5ms
Logitech G500 mouse, K120 keyboard.
UEFI BIOS divergence from optimised default settings
AI Overclock Tuner [Auto]->[XMP]
DRAM Frequency [Auto]->[DDR4-2933 MHz]
Min. CPU Cache Ratio [Auto]->[40]
Max CPU Cache Ratio [Auto]->[40]
CPU Core/Cache Voltage [Auto]->[Offset Mode]
DRAM Voltage [Auto]->[1.350]
DRAM CAS# Latency [Auto]->[15]
DRAM RAS# to CAS# Delay [Auto]->[17]
DRAM RAS# ACT Time [Auto]->[35]
CPU Load-line Calibration [Auto]->[Level 4]
SATA Mode Selection [AHCI]->[RAID]
Model Name LED Lighting [Breathing Mode]->[Disabled]
SupremeFX LED Lighting [Breathing Mode]->[Disabled]
CPU Q-Fan Control [Auto]->[PWM Mode]