AC noise making Ayre amp hum?

My friend has a high quality system with EMM DAC, Sonus Faber speakers and Ayre amps. He recently upgraded to the Ayre VX-R Twenty to pair with his KX-R Twenty preamp.

His system was working fine until the VX-R was inserted into his system. There is an audible buzz/hum when the amp is in standby, and it gets louder when the amp is powered up (with no music playing). This noise is heard from 10-12 feet away.

To troubleshoot this problem, he brought his VX-R to my place. My room has good AC power with dedicated lines. In my system, the VX-R sounded good and was completely quiet (very similar to my BHK 250). So the Ayre seems to be working normally when connected to clean AC power.

My friends lives in a 20-floor condo with many neighbors and probably noisy AC power. He uses an Audience power conditioner, which has been effective until the VX-R showed up. The Ayre has a rated response of DC – 250 kHz. Is it possible VX-R’s the ultra wide band design makes the amp more sensitive to AC noise (from computers, modems, and other electronics)? Will a P15 power plant solve the problem?