Reducing power supply ripple for GSM modem
I would guess that to be a red herring. You're looking at a signal on the order of 100 MHz, with very low amplitude. I'd suspect that's actually some local radio station you're seeing on your scope, and not real noise. You can help confirm this by putting both ends of the scope probe on the common node of your PCB. If the noise is still showing up on the screen, it's not real.

I'd suggest altering your input voltage. If Vnom is 3.6, give it 3.6 and see if the problem goes away.