[VAC] Car radio

[Susie Hayden]

Way does my radio buzz when the univolt is running?  I just installed a new battery and it is working ok.  I get a reading of 13.64 with the univolt on and 12.86 with it off.  The radio works fine if I turn the univolt off at the breaker.  Is it because I have an old trailer (old univolt, wiring etc) and a new (2000) style car radio?  The radio gets hot when it is on.  Any suggestions?  Thanks.