Question for you 737 drivers.

I was riding in the back of one today in MSP and it was snowing. After we'd been de-iced, while we were taxiing the power periodically came up quite a bit so that we were moving at normal taxi speed holding the brakes with the thrust up to what sounded like about what you'd need for a cross-bleed start (but both were running). This happened about five times for about 5-10 seconds each time.

Does it have to do with the anti-ice system or something? It was -SN at the time.