one of the benefits of V-Brakes, helps keep the rims true

I've seen tires that wobble to the left and to the right a little, but I'd agree with everyone else, if you're doing jumps with stock wheels they are probably out of true.

It might be tough to eyeball trueness if you have disc brakes. You could try gripping the fork firmly with your hand and pointing your index finger at the rim until its like 1mm or so from the rim. then (while firmly holding your hand in that position) spin the wheel, if it intermittently touches your finger, your rim is out of true.