If it is anything like my Hornby 08, this could be a tight brass bearing on the top of the bogie gear tower, for the steel shaft carrying the worm. On my 08 these made the loudest noise I have ever heard from an OO loco, like a small girl screaming. Eliminated the problem by lubricating the offending bearings with 'brasso' to give a little more clearance, flushing out carefully afterwards once I judged there was sufficient slack.
A good test if what I have described fits with your experience: to see if it is a tight bearing, run the loco with the top off until the screaming starts. Is a bearing hot? (On the 08 one of them got hot enough to blister my fingertip.) If you have a suitable plastics compatible aerosol spray lubricant (I use GT85) apply this to the suspect location while running and making the noise. If this is the problem and you hit the right spot the cold spray will kill the noise instantly, and the noise will resume as the fluid component of the lube evaporates off, after a minute or thereabouts.
A good test if what I have described fits with your experience: to see if it is a tight bearing, run the loco with the top off until the screaming starts. Is a bearing hot? (On the 08 one of them got hot enough to blister my fingertip.) If you have a suitable plastics compatible aerosol spray lubricant (I use GT85) apply this to the suspect location while running and making the noise. If this is the problem and you hit the right spot the cold spray will kill the noise instantly, and the noise will resume as the fluid component of the lube evaporates off, after a minute or thereabouts.
