Kenwood: Kenwood TS-480 issue

[vsp5151]

I occasionally operate a Kenwood TS-480 at a remote emcomm site. When I first turn on the radio I can get no squelch noise when I turn the volume up and the squelch open. I am operating in Hf mode 80M LSB. If I remove the antenna connection I immediately hear squelch noise. I put the antenna connection back on and still have squelch noise and I can receive QSOs I am a new user on this radio and don't know if I am doing something wrong or if there is an issue with the radio. The radio is not in a climate controlled room and it gets very hot in there. I will measure temperature today and post that information later. I can only stay in the room for about 15 minutes at a time. It has been in this environment for about 5 years and gets operated once weekly for Winlink Wednesday. Any thoughts, ideas or suggestions? climate control is not possible for this room.