I think this is pretty typical for these types of raidos...
Mine does it as well and is relate to the temperature outside...
Unfortunately, they are not the greatest radios and I fully expecto n having to replace it if I end up keeping my car for a long time and not trade it in on something newer in a year or two.
There are some places that repair these types of raidos, I know there is some guy on ebay out of florida that repairs BMW raidos specificly.
2008 328i E90 Jet Black:6MT:Premium:Sport:Walnut/Black interior:Xenon:MTEC V3 AEs:19" Beyern Mesh:35% Tint:Blacklines:OEM Front Splitters