No AM radio (not broken CD player)

[BenV70D5]

Hi all,
I recently purchased a 2008 V70 with the high performance sound system.

Unfortunately there is no AM radio signal, FM is fine.
I know the normal problem is the CD player unit but this has been replaced and since tested (broken when bought it so had a new replacement fitted).

I understand the next culprit could be 1 of the 2 aerial amplifiers (1 in behind bumper and 1 in roof lining). Does anyone have an idea which it could be and the part numbers?
I don't wanna have roof lining out to then find out it's the bumper or vice versa. Can order part in advance too.

Thanks
Ben