Today Islamabad and Rawalpindi got quite some scare of the explosions. Speculations are they could be some supersonic jets.
As geo reports:
Police officials in Rawalpindi say there is no evidence of any actual explosion having taken place. A senior police official in Rawalpindi told he was unaware of any actual explosion, and suggested the sound may have been from jets breaking the sound barrier. However officials at the Pakistan Air Force said that none of its jets had broken the sound barrier today.
If I remember accurately back in 96-97, an Indian jet flied in airs of Islamabad breaking the sound barriers. Ironically, our air forces woke up hours after the incident.
Nothing concrete yet.