SMC1500 Smart-UPS and New Mac Pro - Interference noises?

[Anonymous user]

I have had an APC SMC1500 Smart-UPS for a few weeks now.  It's been working well, and other than a faint constant buzzing it's been pretty quiet.

I just received a new Mac Pro (Late-2013).  Now, when the Mac Pro is connected to the UPS, the UPS (not the computer or speakers or anything like that), is making noises.

It's hard to describe, but it sounds like the power-supply of the UPS is making sounds when the Mac Pro is accessing the disk.  It's almost like the UPS is picking up interference from the computer.

Has anyone experienced this?  I need to move some things around this weekend to see if the noise changes, or if it's due to the load on the UPS.  Overall, the load is only at around 30%.

[BillP]

Have you noticed that the load goes above the 30% when the Mac Pro is accessing the disk? Did you notice any changes this weekend upon re-arranging? It is hard to comment on these noises because everyone has a different opinion I find. I don't think a UPS should be so loud that it is distracting to people but on the other hand, the larger the UPS, the more prone to noise it can be because of the typical data center application. Thus, most UPSs of this type are not geared towards very low sound. This model says 45dba on it's website for sound measurement.

I think if it is louder than the "on battery" hum and clicking you hear, then it is likely not normal. But, it could be caused by a specific piece of load or like you already said you checked, some type of interference on it or that it is causing through your speakers or something. I am not aware of any specific issues with the Mac Pro power supplies. This UPS outputs a pure sinewave too so it would not be due to a step approximated sine wave or anything.

And by what you said, it happens while the UPS is online or on battery when the Mac Pro is connected? Or only a certain mode?

[Anonymous user · Accepted solution]

I don't notice any spikes in the load when accessing the disk.  It's an SSD, so power usage would be very low.

I had some time to experiment this weekend.  I moved the cables around, and tried plugging the Mac Pro directly into the UPS (it was on a strip).  Nothing changed the sound at all.

I happen to also have an identical UPS, so I swapped the units around entirely.  The second unit still makes the same noise, but now it's significantly less than the other one, to the point where I can live with it.

I think it's just the design of these units.