Engine Mechanical problem
1990 Nissan Stanza 4 cyl Front Wheel Drive Automatic 110134 miles

I wanna first say that for years you guys have helped countless people and I think it's AWESOME. My question is regarding a problem that seems new to me with my car....When I start it in the morning and it's not cold here in Vegas maybe 52 degrees anyways I will hear a marble/rolling sound in the engine where the heads are and I KNOW it's coming from there because I used my stethescope to make sure(I'm in college to be a nurse) anyways I will hear this for a few minutes and then it will go away and the usual light lifter sound is there and no more marble rolling sound. Also I was told that the car has a bent valve issue? The car when you start it no matter how hot/cold it is will smoke a liitle white when started only and I may sometimes see a little smoke when driving but thats if I'm sitting at a light for a long time. the ONLY thing I really wanna know is am I gonne HURT the car more by driving it in this condition I can fix it in about a month I'm saving now but definantly don't wanna be stranded. There is NO check engine light on or nothing like that just the sound I stated maybe a slight hesitation once in awhile that I can feel the car doing but I dont drive too far and I do NOT go on the freeway EVER. Thanx alot guys....Melany