Co-incidentally, I recently noticed my SW1600 had a similar problem when I began using the analogue input. A clearly audible "low-frequency white noise" that went up and down with MSR volume. The noise disappeared if I connected the digital input, so I don't know how long it was like that.

I returned it to Meridian, and was repaired for ~�150. It took a few weeks via Sevenoaks/Reading. Completely silent now.

If you're comfortable with electronic DIY, I found it straightforward to remove the (heavy) back panel, disconnect the speaker drive cable (note polarity!) and just send the panel, rather than the entire sub.

Markus