Hayter Harrier 41 Mower Problem

My push Harrier has developed an issue where the rear roller will only move in a forward direction but locks  when you attempt to move it  backwards. Will I have to replace the roller or is there anything else I should look at before embarking on replacement parts. The mower also gives out a buzzing noise if you tilt it backwards to lift the front wheels - I'm assuming this is a linked problem as the engine runs smoothly and still cuts well