Left-right wobble at low speeds

[4.8iS Le Mans_NZ]

It can also vary in intensity between tire brands/tread designs - some don't suffer tramlining as much as others, if at all.
My 4.8is has near-new (20-inch) Toyo Proxes ST-2, and so far there's been no deviating at all, either hot or cold.
By comparison, the 18-inch Goodyear Eagle F1 Asymetric's I had on a previous BMW, always used to tramline when cold, but performed superbly once warmed up.
I've heard that Michelin Pilot Sports are also bad for this.
Regardless, I'd suggest you get an alignment check done, just to make sure everything is within tolerance.