You mentioned AM on the radio, what about on FM.
If it is only on AM, has it just occurred or have you just started to use AM, as AM is usually poor reception anyway.
If it is on FM as well, check the following:
Where is the aerial on your model, it could be a bad or corroded connection at the aerial base. Check the aerial connection at the radio end.
It could also be a loose fuse or a corroded fuse in the fuse box. (unlikely).
Certainly a bad earth is my first thought.
You could try putting a new thicker earth to the radio case in addition to the current one.
It could be a bad earth or fuse link on the blower or window circuit.
Hope this helps.
best regards,
Rustic