Hello skybro6789,   If you did test with minimum to post components and issue persist then it is one of those components. Likely the system board needs replaced. If you do have it running fine except the fans that may be the best you can get without replacing the system board. The Baseboard Management Controller (BMC) controls the fans.  If it is not functioning the system cannot tell how hot things are and default to high.  
Hi, I have two Poweredge R805, and I bought them yesterday, server came showing this error during boot: Baseboard management controller communication failure But it boots ok and proxmox as well as any other os just fine, boots from usb, I can get into the F2 menu (NOT F10 doesn't work) normally. I also both servers give me the same error and I tried reseating everything and no go. Can you please tell me what that error means? and how to fix it? It makes my fans spin at full speed and its too loud when it shouldn't be.
Error: Baseboard management controller communication failure ? Help