Not clear on something ....
HDMI and DP both work on GPU ?
HDMI works / DP doesn't on IGPU ?
i would think that its a bad board since it also gives me a buzzing when i use the GPU, i have tried with 2 different GPU's and they make this buzz when under load. i think it could be also caused by the motherboard. im ruling out cpu problem since the integrated graphics work fine with the HDMI port.