Electricity fluctuations

I live close to the end of the lines at a rural set-up, I have 100' underground cable coming to my house. I installed a 20amp circuit and an 8 gage 35' dedicated line to my stereo. I get current fluctuations that I could not detect through the voltage indicator of my PS 300. I run various air cleaning filters in the house and I hear them slowing down and accelerating intermitently but what bothers me is that I can't use my turtables' power supply (VPI, SDS) at the recomended lowest voltage of 72 volts because the motor stalls. The power company tells me to check the cable that comes in my house but then when I operate the turntable late at night, after 12pm it runs okay at 72volts. It is mostly during peak hours that it stalls. The SDS is plugued in a PS 300. Can anybody tell me what to do to corect this problem? I am handy but not too technically educated.