If you mean you hear low frequencies in the begining and continues to rise in frequencies then it sounds like you may have a shorted power supply. First make sure your ground is ok. Also make sure the signal from your head unit is not the problem with the noise. Does the amp power on? If amp does power on and head unit and all connections to amp are fine then either the power supply or something in the output stage is shorted. Could be a diode, capacitor, resistor, or transistor or an ic chip. Let me know if amp powers on and this problem happens. I repair amps for a living, i'm the cheapest you will find anywhere. If interested send me a private message.
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