Hello, I've encountered a small obstacle recently. I purchased new square taper cranks/chainring, and after installing on the bike, and testing them out, I began experiencing a "bounce" from my rear derailleaur, after every four or five pedal revolutions. I purchased a similar set of new st cranks/chainring for another bike, and the same thing started happening. Both bikes rode fine before this. It's not alignment, nor stiff links. All suggestions welcome. Thanks.