2001 CRV..idling issue..forward/back movement and clicking

As the title says, my lovely 2001 auto crv(that now has 138k) I bought a few months ago used from a dealer is having a bit of an issue while idling. This only happens occasionally, only after i have been driving a few miles at least and seems to be getting more frequent. There is a noise coming from the front of the car sounding a bit ca-chunk like along with a slight forward and back motion. Both go away after a few minutes of idling. I know this is a very vague description, and the car is running great other than this, I just dont have any ideas of what this could be so any suggestions of things I should check out would be much appreciated! THANKS!