I have a Cobra 2000 GTL purchased used on Ebay. When I turn it on the speaker emits a loud tone. The volume control does not affect it. I can still hear other stations, but the tone overwhelms them. I tried every speaker jack. SP1, SP2, Aux, even the headphone jack. The speaker select switch was tampered with. i think someone tried to add channels to the MB8734 chip, so i disconnected the jumpers and it still does it. Anyone help is appreciated. I want to restore this unit and this seems to be the only problem it has.