"When front tyres were replaced recently the tech remarked he felt the bearings were 'a bit loose'."

Others may disagree but I have never had to replace them. Repacked them whenever I had time or I had the front brake discs off. These are serviceable bearings that anyone old enough to remember parachute pants (and works on cars) should know how to service.

Your noise is more likely to be the driveshaft center support bearing, tranny tailshaft bushing (if automatic), slowly failing M47 transmission (if a TRUE 5-speed manual).