James, have you had the unit make any grinding noises especially just after opening and closing of the doors? I had this problem with the same fridge/freezer (which I still have) and the problem was caused by the mechanism which spins the blade on the Evaporator Cover. Basically the blade gets frozen over and when the unit trys to turn it the cogs etc end up grinding together as they're worn.
I had an engineer fit this
http://www.4mysamsung.co.uk/cgi-bin/product.pl?PID=1226999§ion=111068&brand=&model=RL33SBNS&path=111066,111068
for me back then. Mine's is making the same noise again and it's only a matter of time before the lights start flashing!
Seems pricey assuming that's what's causing your problem but have a go at fitting it yourself instead of calling an engineer. To take a look at the blade and see if it's blocked/frozen take the drawers out of the freezer and remove the panel on the back wall inside the freezer. The Evaporator Cover is located behind that cover. There's a few screws and a couple of plastic clips which require a bit of elbow grease to prize out.
Obviously make sure the unit is unplugged from the mains before trying it!
Dougie
December 2010