Now this is getting interesting. I understand the issue now. May Fl. Keyclick be what you are getting instead of Breath Noise? I took a look at the manuals and that's what the capital tone is at instrument number 122 for the SC-55. For the SC-55mkII, Breath Noise is the capital tone and Fl. Keyclick is at variation number 1. Normally when they add new tones they never swap them with capital tones, but store them in the variation banks to provide backwards compatibility...
But clearly Breath Noise does come up in the General MIDI specification just as I said. You must have a SC-55 without a GM logo then. There are SC-55 units (NOT mkII) which have the logo, so it would be interesting to know how those behave in this case.