Interesting comments.
It might be worth noting that that hum-dinger was invented in order to get round a problem that noticeable at the time.
Modern low-noise systems can be expected to be very much more sensitive than those of ~75 years ago, and might be subjected to effects that were undetectable back in those days. Could it be that bonding the neutral line to earth unbalances the mains wiring, leading to residual effects that could be detected?
The ADSL broadband system works as it does because the two-wire system is balanced. Adding imbalance at the consumer end, an all-too-often occurrence, can lead to severe MW pickup at night, and during the day if close enough to a MW transmitter, leading to some combination of lowered noise margins or connection speeds.