I just bought a mid-2000’s Dual Rectifier (3-channel) and it sounded OK when I tried it out but after the long car ride home When I turned it on at home I found that any time I hit a chord (or note) on channel 1 while in pushed The output changed to a hug pitched whistle/squeal. I checked my connections, etc, but finally realized that the squeal “followed” the channel 1 gain control. When I’m playing clean there is no squeal, but is soon as I push it over to pushed I find any amount of gain above about two brings about the loud squeal. If I start out with no gain and start playing and slowly turn up again at about 1/4 the output turns into a squeal and that squeal only changes in pitch the more I turn up the gain. What the heck is happening here?