Getting to the rumbles is actually quite simple. After you pass the first checkpoint (go there if you passed it), go to the right. You'll notice a mine cart; push it/ride it as far right as possible. Then, push it to the left until it stops against the slight ledge (beside the sign in the floor that tells about the mine cart). Climb on top of it, then jump up, and there should be a rope you can grab. Jump to the next rope, then the chain, and then onto the platform to the right with another mine cart.
Push this as far right as possible, off the platform. Jump down to it, then push it as far left as possible. Pushing it may be tricky at this point, so just jump on it and hold your keyboard's Down arrow to accelerate. Keep pushing it left until it goes under a wall and then stops at a wall. Jump on the chain above, then up onto the platform, then onto the platform to the left. Fall through this one and the three chains beneath it onto the mine cart. Now jump onto the ledge to the left. Enter the next room, drop through the platform, and proceed to beat the series of rumbles.