Can't Read Disc Error??

Ok, I am on my 2nd 360 after hearing a scratching noise, and getting the error 'Can't Read Disc".  Tonight it happened with my new 360. 

I looked at the disc, and it was clean.  Is there something I should get to clean the discs with? 

Is this a known issue?  Is there anything to completely stop it? 

When you are online, it boots you off, and you get a DNF because of it.

 I read that if you lay your 360 down flat, this will happen less often, or never. That's how I do it, and I've never had that problem.