If you have SAS cable is connected to rear bay can you remove that and check the behavior? If issue still observed you can try removing rear backplane also. You can refer below link for instructions on same [URL]   
I have an R730XD. It has a rear flex bay which is not actually in use. Directly above the bay, I have installed a full length PCIe card in riser 3. Its heatsink touches one of the BP1 cables, so I removed them (both the power and signal cables).I get the F1 prompt about BP1 being disconnected. Is there a way disable it in settings, or do I have to physically remove the rear flex bay/backplane?
Disconnect/disable BP1 in R730XD