Dirty rims.
There is a brand called "No Touch" that works very well. They make one for tires and one for wheels. And if you really want to touch the wheels to scrub them, you can. If yours are that bad, it wouldn't hurt.
I really like Eagle 1 All Wheel spray. Used it for years with good results and no wheel damage. It gets off superficial dust with just a rinse but it works great with a soft brush to help it along
the best stuf to use on dirty rims that have brake dust and what not is break cleaner it penitrates and let sit 1min and than wipe off with wet rag and than wash the rest off with soap and water thats what i find to work the best



