My Ampeg BA-110 hisses and hums when I use the 0DB input. The amount of hiss is similar to a high-gain guitar amp with the gain cranked. Just plugging a cable in is enough to make it noisy, plugging the cable into a bass makes more noise, and touching the bridge or strings of the bass makes it hum like an ungrounded Stratocaster. The -15DB input is fine, it makes no more noise than the amp does with nothing plugged in. Is this normal for this amp?