It's common on most AC systems for the compressor to cycle on and off. That's part of how the system regulates. The radiator and / or condenser fan motor will turn on at the same time the compressor is on because that's when the heat is being generated that must be dissipated. You may be feeling the bump of the compressor cycling on. Many people interpret that as a transmission shift. For some models there was a modified engine mount that improved how it absorbed that bump so you wouldn't feel it.
You know the fan relay isn't defective because if the fan runs, the relay has to be working. The fans will never run all the time. People already whine and snivel that they can hear the fans at low speeds so the engineers responded by incorporating all kinds of unreliable and expensive computer controls and variable-speed devices. Those "improvements" cause more trouble than just using a switch to cycle the fans on and off.
Tuesday, August 27th, 2013 AT 11:43 AM