Generally no. MIDI was (smartly) designed and implemented with a device known as an opto-isolator or opto-coupler in transmitting and receiving MIDI ports. Since the data flow of MIDI is opto-isolated, there is no electrical contact at the MIDI connection points, which eliminates the potential for a ground loop, or at least eliminates MIDI as a cause for a ground loop. Of course this doesn’t do anything to solve your audio and electrical connections, not to mention the fact that, by racking items in a rack, you usually are connecting their metal cases together, which can aggravate certain ground related problems. Items in a rack can be isolated, but that’s a tip for another day, and one we’ve covered in the past already.