Solved: Poor AM Reception in Car.

there probably isn't much that you can do, except take it to an auto electrician to see if they can tweak or change the antenna and /or the actual unit. BUT am is gradually being phased out as DAB is being introduced and FM will also go before long and many car radios just won't pick up a weaker AM signal. Recently BBC have reduced power on many AM transmitters and switched some off, so they can start switching to digital radio

It is very likely though, that a good auto electrician or radio specialist can add a couple of tweaks to cut down on some interference that you are probably getting on the AM band in your area.

Most newer car radios will only have inbuilt suppression for FM frequencies & not AM and if the car is putting out spurious interference, from something electrical, then it needs to be suppressed. It might be as simple as moving the route that the antennae wire takes from the radio to bypass the wiper motor or heater motor, or it might need a lot more work, with the antennae replaced or moved to a different position on the car.