I had a similar problem at our new site. We had a permanent service installed with a temporary outlet panel, (we're building our retirement home here), and when I tested the outlets, the tester showed a weird flickering, between hot ground and normal. I put a 12" steel peg in the ground, and showed 25.6 VAC between ground and the peg. Service tested OK. Opened the outlet panel, discovered that whoever built it took a shortcut, none of the outlets had a ground wire that went to the panel ground cable. Instead, they had just grounded to the outlet box and counted on the metal conduit to be a ground connection. I installed ground wires to each outlet to the panel ground, all readings dropped to zero volts from peg to ground.
You have to be careful with rural power systems, our power company has neutral attached to a deep ground rod, which I verified is carrying our return amperage. My service ground is also attached to a deep ground rod 50' away from the power companies neutral connection. Both penetrate to local groundwater level, and with the salts in our soil, make just about a perfect electrical connection, .3 ohms. I did confirm that my ground connection is carrying no amperage.
2012 Jayflight 28 BHS
2014 F150, 5.0 L, 3.55 axle