see title- ran the AC for about 40 minutes on the ride home tonight, when I put it in park and turned the ignition off the engine gave a resounding *clunk*

fearing for my precious CRX I turned the ignition back on and it took longer than usual to turn over- cut the engine again, same *thud*...I drove it around the block with the AC off and parked and no thud of which to speak...

I'm leaning toward a belt issue- any ideas? I've had her for about 6 months and this is the first issue I've had (also the first time I've run the AC for more than 10 minutes)