Good stuff so far, especially Sean and Rap. One thing is certain - having two separate ground systems (power system and ground rods) will cause trouble, especially with a 15v difference. It's not a component problem.
So pick your ground system. Either float everything and tie everything to the ground rod, or give up on the ground rods and use the power system ground. If you use three prong cords and tie to the ground rods then that 15v difference results in current flow through the ground paths (chassis, cabinent, etc) through the ground prong to the power system ground.
I don't know how old your house is, but I wonder if the power system ground is good. Sometimes you get corrosion in old electrical systems.
With your audio gear referenced to ground rods, you might get a slight tingle if you come into contact with a component chassis and some other appliance referenced to power system ground (like a metal lamp with a 3 prong cord) at the same time.
So pick your ground system. Either float everything and tie everything to the ground rod, or give up on the ground rods and use the power system ground. If you use three prong cords and tie to the ground rods then that 15v difference results in current flow through the ground paths (chassis, cabinent, etc) through the ground prong to the power system ground.
I don't know how old your house is, but I wonder if the power system ground is good. Sometimes you get corrosion in old electrical systems.
With your audio gear referenced to ground rods, you might get a slight tingle if you come into contact with a component chassis and some other appliance referenced to power system ground (like a metal lamp with a 3 prong cord) at the same time.