I have a sony strde845 reciever . It runs on either 4 or 8 ohms. While watching a movie or listening to music it will sometimes make a clicking sound and either my center or my rear speakers shut off, now if i press on the front of the reciever it will sometimes click back on. I was told it was a gronding problem with the back plate of the reciever and i should tighten all screws on the back. It still screws up, whats the deal does anyone know.