For days now, I’ve been getting intermittent buzz when recording using the following gear: Rode NT1 direct into Focusrite Scarlett Duo, into a laptop (Acer I5 running Windows 10) running Audacity 2.3.3. The buzz is relatively slow (that is, it is not a hum). It’s a bit like a two-stroke petrol engine you might find on a model airplane but very quiet (about -20db when it gets bad). Deactivating phantom power gets rid of it for a while, then it comes back. My input levels have to be quite high to get a decent recording level: the gain nob on the Scarlett is set at about 3’o-clock (75%) and audacity is set to -0.86. The buzz seems less intrusive when the laptop is on mains power, and not on battery.
Any ideas? 
In advance, thanks for your thoughts.
Does it seem to be coming from the mic or mic cable? (Does the noise change when you move the mic cable around?) It could simply be a broken shield in the mic cable…
Or, does it go-away when the mic is unplugged?
Sometimes with USB-powered interfaces, noise gets into the analog electronics through the USB power. The fact that it changes when switching between mains & battery power might point to that problem. But usually that’s a high-pitched whine… Probably higher in pitch than a model airplane engine.
Another “hint” would be if whatever the computer is doing changes the noise (such as if the hard drive is running or when the display changes).
If you have a different computer available, try it. Or maybe a powered USB hub would help.
My input levels have to be quite high to get a decent recording level:
And the knob adjustment does affect the noise level, right? There are a lot of factors, starting with the loudness of the sound hitting the microphone, the microphone sensitivity, and the gain of the preamp (in the interface).
The NT1 is a “hot” mic. Condenser mics have higher output than dynamic mics and the NT1 has higher output than most condensers so that’s working in your favor (for a better signal-to-noise ratio). According to the specs it puts-out a signal 27dB higher than a Shure SM58 (dynamic mic)!
Thanks for that DVDdoug. I’ll try a different mic cable and a different laptop. Your comment about digital and analog components interfering is apt. Switching phantom power off and on seems to give temporary relief. Will also check memory and disk usage when the buzz is present. 