That's what BBC says too....
dad says it was very loud. But there's no bomb, neither an after shock- so it's either some really obese gentleman passing wind, or it's a sonic boom. Afghan attacks in NWFP cannot possibly be heard from THAT far. And first reports said that the blast was heard from close to the Airport, and windows broke in THAT area.
@punk & all other ISB members:
Any windows breaking or something of that sort in E9 or anywhere in ISB?
If a blast from NWFP broke windows in rawalpindi, then it had to have broken windows in ISB, and the sound (theoretically, therefore) could also be heard in Lahore. What are these guys trying to feed us...?
It's a sonic boom.