RFI can be elusive to deal with - some setups work nicely, others have a lot of interference, its all due to the complexities of antenna design (in fact, accidental antennas can be present in a particular piece of equipment by chance, which resonate at the particular RF frequency of interest. Sounds like you have a solution though 
Incidentally GSM phones are particularly bad at generating interference because they use time-division multiplexing, sending pulsed packet streams which cause morse-code like interference on many audio devices.