I assume when you use the term "light rail" you are talking about BART.
See http://g.co/maps/bvzh6 for a map I created showing the Bart tracks, and proposed Warm Springs South BART Station (Roberts is to the left of the blue icons).
Also, while it's always best to experience environmental conditions personally with your own two ears and eyes, here's a sample â€œenvironmental noiseâ€ video I shot for a client just north of the Fremont Station: http://youtu.be/pGix303gpSE
The future BART tracks are approx. 400' from this home. http://goo.gl/maps/XOZWW
If noise is a concern, you may want to find an area where the active BART track is ~400' away to approximate the sound level.
I didn't realize we were talking about BART. I thought the question was referring to JB's Madera to Bakersfield multi-billion dollar high speed rail system. With our State's current debt service I hardly think we need be thinking about HSR until we get out of this mess which I don't see happening anytime soon. But then that's just my built in cynicism at work.
BTW, I think I mentioned that Janis and I would be visiting SF from March 2-8? Let's try to meet up somehow.