Rubbing noises under 2005 Jeep Grand Cherokee.
 

I have a 2005 Jeep Grand Cherokee and often while the engine is idling, it makes these rubbing noises wit a few pops. The noise stops after every few seconds and returns after every few minutes of idling. The transmission system seems to operate well when driving but the noise still persists and seems to go on for longer and returns with more frequency. I feel and hear the noise coming from right under the vehicle each time the engine is on but it's not coming from the engine compartment but under. Any ideas of what might be wrong or going on with my SUV please?