weird knocking noice

Once in a great while I get 3 knocking sounds (real close together) coming from under my car. Usually it's when I have been driving for a while and stop at a stop light, or at least that is the only time I can hear it. At first I thought there was something rolling around in my trunk, but I have check and theres nothing there. As of right now there are only 2 things wrong with the car that im aware of. The 1st one is my engine light is on and it says I need to replace my EGR valve, the 2nd is my fuel gage has stopped working recently. Is there something I should be looking for?

It doesn't always make this sound, nor can I get it to do it when I'm on the out side of the car to figure out where it is coming from. I drive 30 miles a day to work and another 30 miles home and I might here this about 5 times a week. The sound is not real load, and sound like it is coming from the rear of the car. Just want to make sure if something is going out I can replace it before I get stuck somewhere.

Thanks for your help.
Lonnie

im not a mech. but i have a 02 monte w/3800 eng . that was doing similar to the same thing on the knock/pop noise replaced the egr valve and that noise went away . i responded to see what your gas gauge is doing i have a 05 impala that i started having gas gauge problems with this week sometimes it reg. right other times it goes way past the full mark .. good luck hope you get it fixed..

I have a 2000 impala and just noticed the same noice. I also know it must have something to do with the fuel tank because when I fill the tank full the noice is gone but when the tank gets to be about 3/4 or alittle less it makes that noice when I stop and go. I haven't had the chance to check it out because of the cold weather . ( I don't have a garage just a shade tree )

hello on the guages its the stepper motors i ordered four from the internet 21 bucks ebay. the only thing i didnt do was remove the soldering and soldered it back but i just wasted 30 bucks total it was a friend my speedometer and gas guage had gone out well i bought it like that i google it and fix it its real fast and simple and verything works now i also replaced the temps one it would probably had gone out later but it happens beacause of a faulty stepper motors from gm from 2000 to 2005 i belive i dont think there as been recalls for all models only some and i think you have to have less than 80000 miles or something like that. hope it helps