ford transit 2002 t280?

got problems starting my ford transit t280 sometimes it will turn over but there is a grumbling sound from the battery and the central locking system goes haywire locking and unlocking when engaging the ignition other times all i can hear when engaging the ignition is the solenoid click and no turn over from the motor i have changed the motor bought a new battery cleaned the negative earth from battery to chasis and earth from solenoid to chasis pretty much checked everything just wondering if enyone else has experienced this and what was the outcome the starter motor is working fine as is the solenoid when i bench checked them any help would be appreciated