hifi engine

Mini Chai ne Aiwa serie 22

I recently bought the Aiwa Mini Series 22 series and still have a problem with its fidelity.
There is a slight distortion on the bass sound, both in Tuner and CD input.
I could not determine if the problem comes from the preamplifier or amplifier.
I am not leaning more for a problem at the amplifier level.
Could I be advised in the search for the problem?
thank you in advance.