My guess is the waves are caused from the old roof that is underneath. If the waves are just minor waves where the upper layer of shingles are conforming to the shape of the underneath shingles, you probably are fine. Waviness is the nature of the beast when you are dealing with a roof-over. It is a bit unsightly, but unless the waves are excessive, your roof should be OK provided it is still adhered tightly to the shingles underneath.
BUT... if the shingles are curling up around the edges, or you have bald spots where the sand granules should be, then I would suspect the roof to be older than your 10 year estimate and in need of replacing soon.