As a matter of course I have re-installed Windows on both disks as this Windows feature works very well and preserves all your old settings, but that didn't change anything. I have also used UBD to rewrite MBRs etc but that hasn't changed anything either. Both disks are Seagate with the original being 200Gb (4+ years old) and the new one being 2Tb (8 months old).
I sometimes don't switch on this computer for months (unplugged) and it still keeps the time so the clock should be fine.
The old disk is still in this computer and I can still boot off it, I'm using it as an online backup until it dies. Booting into either Windows system exhibits that same pinging sound from the hard disk as described in my original post. I just can't believe I have two disks that have faulted in the same way, it must be remnants of that virus I neutered some years ago, if only I could recall the name.
Symantec antivirus doesn't work
Sage advice, it always looked like marketting fluff to me. Can you recommend another (not AVG, found the free version to be a waste of time). I have been impressed with Trend Micro in the past, not sure if that's still relevant today.
I really don't want to upgrade this computer as it's fulfilling my business/household needs very well, I'd just like to get rid of a potential problem that may render it useless. I will eventually upgrade it in the future and my plan is to buy another powerful (expensive) computer of the era and convert my current computer into virtual form as an interactive backup.