Why is my QuadDAC giving distorted sound?

QuadDAC gives me distorted (sounds like blown up subwoofer with all headphones, even low impedance ones) sound at maximum volume if I don't remove atleast 4dB of volume using L R sliders… And also, if I rotate or move (seems to have space inside) the plug then strong, loud static noise happens… Qualcomm DAC has zero issues, no static from jack or distortion… I think it is headphone jack issue, but I don't know, as DAC mode gives distortion in bass (only high volumes), so it may be DAC as well… What is the issue? Is it jack or the DAC (which seems somewhat better than Qualcomm)?