Yeah.. Boeing tried this back in 68. Didn't work too well because people didn't (and arguably still don't) understand sonic booms/LEO/Parabolic flight. I've got my doubts on this one, especially with the eco-nuts out there..
They've been working on a silent SST since the 1950's when they began the Valkyrie program. Problem was that it wasn't economically feasible to build a silent SST when they spent almost $600 million in 1960 to build one Valkyrie. Tools and materials have changed considerably since that time.
Today we have turbofan engines that support supercriuse at Mach 2 and can power an aircraft to Mach 3, turbo-ramjet engines that can supercruise to Mach 5, pulse detonation engines that can do well in excess of Mach 8, cryogenic aviation fuels, cryogenically cooled airframes, superalloy materials capable of withstanding over 5000 degrees Fahrenheit of heat and not weaken rather they get stronger, and fabric materials that can take any shape and have more strength than Titanium. The tech certainly exists today to make an SST very economically feasible.
As for that crap about no one understanding things about sonic booms, LEO, or Parabolic flight, that simply isn't true. How do you think any of the planes in the X program from the 50's and 60's flew? Thats right Parabolic or LEO flight paths. And it was from the X program that they figured out how to make an aircraft weaker than a typical supersonic airframe and get it to go faster than the typical supersonic airframe through the study of the effect of maximum dynamic pressure, or Max Q.
They have already produced "quite" sonic booms. Dryden Flight Research at NASA did testing for Boeing on an attachment to reduce the noise of a sonic boom and it worked quiet well. It was a 15' long needle attached to the front of an F-15 and it created multiple pressure waves that significantly reduced the overall noise generated by the sonic boom.
They've been researching an SST for almost the last 60 years. Something tells me this is less of a pipe dream than you think.