I have had excellent service from my Skyview Touch/Flightcom 403/Garmin SL40 system for the past 3 1/2 years and 270 hours. Now I am experiencing several issues and the situation seems to be deteriorating. First, I am hearing a buzz in the intercom that is sympathetic with engine RPM, and seems to get louder at low RPM. I can stop the hum if I turn off the SL40. Second, when I first turn on the avionics the SL40 will transmit just fine, but after it warms up a bit, I get a very loud hum when I transmit. These conditions are making the comm system almost unusable. My guess is that the SL40 is going south. If that is tie case, where do I go from here? Thanks for your thoughts, and I am sure that I am not the first to experience these conditions, but I have been unsuccessful with my searches on the subject...........Tom