Distortion and popping from new speakers


I have a problem and need some advice. I just purchase a new system from Audiogon members that now consists of new Opera Quinta speakers, a used Musical Fidelity 3.2 Int. Amp and MF 3.2 CD player. Also purchased Purist Audio Vesta speaker cable, Silver Audio interconect and a Zu Cable power cord. I have listens to the new system and it sounds good EXCEPT when I turn it up to about 45% power or about 11:30 on the volume knob. That is when the speakers will start distorting and making a popping noise, I just turn it down below 11:00 on the volume knob and it sounds good again. This is not normal is it? I have tried different CD players, interconnercts and music but that doesn't change things. What should I try next?
davef
Thank you Plato for you research and analysis.

I will enjoy my new system and it does sound great to me.
Sounds to me like your AC line is below the 120 V reading with so many gear plugged to it, try to disconnect everything and just plug one source at the time, or feed your amp from other AC outlet which is not in the same route of the rest of the system.

Fernando