I think the interference clicks may have come in from the internet cable running past the power supply for my speakers … It’s a big chunky power supply and the cable was running straight over it. I bet touching cable to the earth on the modem was creating a loop between the psu and the modem.
The cable running over the psu was probably picking up the magnetic field and having a current induced into it and when the current was interrupted by the cable being grounded, that’ll be when a spike clobbered the bit I think got fried.
I’ve moved the cable now, it doesn’t touch that psu any more 🙂
Modem’s still going strong, Internet Bloke was actually glad to see one of that type – the newer ones aren’t very good apparently. Linksys seem good, although my dad’s one needs fixing again.