Sounds like the amp is oscillating. I think looking at the 12VDC and ground connecton to the amp is in order. For a 1000W high quality amp, it is vital to have good ground and 12VDC conntections, preferably with a big filter capacitor at the amp ene.
Of course, the amp could be defective or the speakers hooke up wrong.
Paul
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the 1derful1