Technics SA-GX5OO Receiver

Question

I have a technics sa-gx 500 it works great but after it's on for 2+ hours the display locks up on me when I try to lower the volume with the remote, also the volume locks up when I try to lower it, sometimes if I raise it then lower it it will go down otherwise I must do it manually. I also get a strange screaching sound through the surround speakers when ever I change the volume level every time I press the remote volume button. Any ideas what's going on?