Weird audio concern

I recently got my iPhone 5 and have noticed intermittent audio distortion out of the headphone jack.
My car has an ancient tape deck (factory Acura head unit) and I have a cassette adapter in there to hook into my headphone jack. (It's a nice one from monster)
While driving today I noticed my pandora sounded awful through the car. I didn't change anything except swap my wife's iPhone 4 in its place. No more distortion. The crackling sound wasn't constant with my phone though. It would play about 30 seconds then crackle for a few notes. I have the volume on my phone set to the same aproximate level as my wife's, less than 75% since I've noticed that can affect its performance.
So I come home, listen to pandora over my apple ear buds and don't hear it at all.

Has anyone had an intermittent audio quality concern like this? Maybe my phone just doesn't get along with the tape adapter, my previous 3GS did and obviously my wife's 4.

Thanks
Brad