I have the same rig, installed in my car and it has experienced the same problem.
When I purchased the radio from a guy on eBay, it was a bargain price but advertised as 'like new'. In fact, it was "like new" and after installation in my car, with a new 220 antenna all was good. But within days, the RX starting making some noises which sound more like a loose antenna connection, or a bad antenna connection. Since it was just installed I wasted some time troubleshooting antenna problems when in fact it was the radio.
Anyway, after some troubleshooting of the radio, it simply turned out to be dust or "stuff" that worked it's way into the chassis. Apparently the SMT design and dirt, dust, or particles that get into the thing created just enough havoc that the RX sort of "crackles" (for lack of a better description).
All I did was remove the top and bottom of the chassis and blow out / clean the internals. This was about a year ago or more and the problem has not returned.