buzz from one phono preamp more than another?

Check your cartridge clips if they're connected properly.
Any clip weak or loose?

You might also want to check the RCA's on your interconnects to make sure the pin is firmly engaged by gently putting pressure on them in a circular motion. If the hum disappears either completely or intermittently during this procedure, you probably found the source. Standard design female RCA's are notorious for this. A very worthwhile upgrade for any component in my opinion is to replace them with WBT's which have a two-piece spring-loaded receiver that clamps down on the pin.

The Lehmann uses a toroidal transformer in its power supply, and toroidal transformers don't react well to dc offsets that may be present on their ac input. A common symptom is mechanical buzzing that is emitted directly from the transformer, but I believe electrical noise can also be introduced into the power supply circuits as a result.

I would suggest placing your ear near the power supply and listening, with the room otherwise quiet. If you hear mechanical hum being emitted, I think it would help to confirm that theory. In which case, search prior threads here under "dc offset" + "toroidal" for suggestions on how to deal with it.

Also, if there are any dimmer switches in the house, turn them off. They can introduce dc offset, noise, and other anomalies into the power lines, as well as radiating emi/rfi through the air.

Regards,
-- Al