Hi 

I recently purchased a Toyota alphard 2006 that's been  converted into a camper van.

I have noticed a strange grinding sound when I sometimes have it in reverse especially when I am going up an incline. When I put it back into neutral the sound stops

Any suggestions as to what might be causing this

could you pm me your reg no. i might know what it is just need to double check somthing

Yes mate it's RY56TUU 

ok first things you need to check your brake discs  they may have a high spots if warped check your pads 

Check your drum shoes. Mine did the same and found the retaining pins had snapped.