About 2 miles from home, noticed steering very heavy turning right at a junction - then, a very loud squealing/chirruping from the engine, related to engine revs. Sounds a bit like that slipping fanbelt thing you get in the winter. It's a 1.9JTD 16V with a remap.
Got home, opened bonnet and had a listen. Seems to be coming from offside/rear of engine. I think the heavy steering thing was a red herring, the steering fluid resevoir is full and there is no noise upon turning the steering wheel. Maybe the engine nearly stalled and caused the momentary heavy feeling?
Slightly strange smell coming from engine bay, no smoke or anything though. The engine wasn't overheated and all fluids are at full. I immediately thought 'turbo', but that is at the front of the engine, down below.
My second thought is maybe the timing belt, although that's only halfway through its life (hopefully), the car has done 90,000 miles and it was changed at 60,000.