The H9 should unbalance any balanced lead connected to it, so this is probably not the issue.
More likely, you have some kind of ground loop. This likely needs some skill and experience to diagnose, but you could try unplugging things one by one to see what makes a difference. If you have balanced lines, you could try disconnecting the ground (shield) at one end.
Make sure that everything is plugged into the same power outlet.
But, if all else fails you may need to find a technician to check over your setup. This is not something that can easily be done remotely.
