Thanks all for the responses. So in effect working as designed but also agree with Maby it's an annoying sound and passengers always comment. Will continue to turn the radio up to drown it out, maybe that is the fix.
When our PHEV is low on battery charge and we are driving, the engine kicks in to power the battery (normal operation) however we have noticed that in this instance the engine seems to be running in a high gear and makes a noise similar to running a standard car in the wrong gear. The garage has...