radio on a polaris ranger

I installed a marine radio kit which included the heat unit, speakers and waterproof cover. I installed the stereo overhead on a wooden enclosure I built myself. I have power ran directly to the battery and not to the ignition switch. I used about 6 ft of 12ga wire to run it from the battery to the stereo where I connected the memory and power leads from the head unit together. I used the ground from the HU and ran a wire to the roll cage and connected it to a lag screw in the roll cage. I have no problem sitting in the vehicle at idle, everything seems to work great. When I push on the gas and move the vehicle the sound goes out until I slow down to come to a stop it comes back on. I double checked on my connections and everything seems to be secure. I even shook the vehicle by hand vigorously while idling to see if there may be a loose connection but the radio continues to play with no problems. I sent the first stereo back and installed the replacement but I am having the exact same problem as I did with the first one. Does anyone have any advice on how to solve this problem?

Most likely a voltage problem.  Check your constant voltage while you are, or someone else for safety purposes, drives.

So if the voltage drops with power to the battery directly what would be the fix?

Find the bad connection and repair it. How did you connect the wire to the battery?

Check the ground too, I would look real close at the Lag Bolt. And at the integrity of the roll cage. You may need to run the ground wire to the battery also.

I put a gel-cell battery under the driver seat (with an isolator)
and ran all my accessories to that battery
2008 rhino 700fi