I have 2 brand new Lewitt 550 LCT microphones plugged into the RME Fireface UC audio interface using XLR cables. The interface is plugged into a MacBook via USB cable. There is a constant humming sound in both playback and during recording. I've tried the following tests:
- I plugged in 2 Neumann mics into the interface with no humming issues on any laptop.
- When I plug the Lewitt mics into a Zoom handheld recorder there is no hum.
- When I touch the Lewitt mics while plugged into the interface, the hum quiets down slightly.
- I've tried using the Lewitt mics and the interface with the following laptops: 2 Lenovos (it produces no hum), 2 ASUS (it produces hum), and the MacBook (it produces hum).
Here is a short clip of the humming sound: http://vocaroo.com/i/s0FPE1nDasAJ
EDIT: The above clip is when the MacBook is on battery power. When the MacBook is plugged into the wall, the hum is greatly reduced but it is still there.
I would greatly appreciate any tips that will help me get back to recording. Thank you very much.