I tow a Ranger 188vs on a Ranger Trail single axle trailer. Last year a blew out a bearing and since then I've replaced the tires with new Carlisles, had the tires balanced twice and installed new vortex wheel bearings. When I reach 60 mph I start to feel a vibration that occurs in a consistent cadence. It will vibrate for about 5 seconds, stops for a few seconds, vibrates for 5 seconds, stops for a few seconds, etc. I've towed it with my neighbor's truck with the same result so i think I've isolated it to the trailer but I don't know what's causing it. Any thoughts out there?