Engine Rumble at Start Up !?

Just got my first Mazda Protege' 2000. 94,000 Miles on it. I don't know if this is normal or not.  I just bought it from a friend who had the Powertrain Warranty up untl about 6 months ago. So he did all Maintenance up until this point. Here's my concern. When I first start the car and I take it out of Park and put my foot on the brake, the engine rumbles pretty loudly until I let go of the brake & drive. Then it is quieter than a mouse and it runs just fine. It's an Auto Transmission by the way. It also does not seem like it's going to stall when this happens, more like it's going to take off. :) It may be just me being paranoid because I have no problems once I am driving. Thanks in advance !

Give a check to the rubber hood stops at both front corners. Your description sounds very much like a hood rattle. When you start it back up tomorrow morning and put in gear with foot on brake and noise is present then pull the hood release. If noise stops then you have found the culprit. The rubber bumpers are adjustable. Rotate each counterclockwise 1/2 turn or so untill noise is gone. Hope that is all it is anyway.

Thanks Babyhuey. I thought it might be because the engine was still cold. But that's a great thing that I would never have thought of to try. Thanks.

I tried the Rubber Hood Stop Test this morning. That's not the problem, if there even is a problem. Again, I'm not use to these little engines and how they sound at Start Up. I owned a 1990 Caddy Seville with a V8 before this. :)

Someone suggested Engine Mounts. But wouldn't it Rumble ALL the time, if it were those ?