I've had a similar problem from time to time with my FSG-50, every now and then a burst of noise. Eventually I realized it was only happening in the circuit for runway 25 at my home base, at about 2/3 of the way on the downwind leg. It hasn't happened this year so all I can thin of is that there may have been some equipment at the storage and construction yard beneath the downwind that was putting out electromagnetic interference. This happened with the original avionic setup (Peschges VP-4E Nav), when I added a Colibri logger and with my current setup (LX8080 Simple, V5 vario, Powerflarm Core and FLarmview 57) so the rest of the equipment doesn't seem to be a factor.

The radio is pretty sensitive - I've been at 2,000ft. ASL (1,900ft. AGL) on a mountain ridge in Hope and have been able to hear transmissions from people in the circuit at Delta Airpark (both airports are assigned the same frequency) 70Km away!

I tried JJ's progressive start up of the avionics with the radio squelch turned off and was pleasantly surprised to find that the noise didn't increase noticeably as I turned on the other units.