MYSTERY BOOMS reported in 2008 -

NORTH CAROLINA - 9/7/08 - Emergency officials said residents in Clayton and Wendell reported hearing loud booms that shook their houses Sunday evening at approximately 5:45 p.m. People in Selma and Middlesex reported the same thing. Emergency crews were searching the area for the source of the noise. Some residents have speculated that the noise might have been the result of a sonic boom, a term that is commonly used to refer to the shocks caused by the supersonic flight of a military aircraft.
However, officials at Seymour Johnson Air Force Base in Wayne County said planes are not allowed to produce a sonic boom. Plus, all of the base's F-15s completed landing at 4:15 p.m. (additional individual reports at link)

MINNESOTA - 8/14/08 - People living in the Longfellow neighborhood in Minneapolis were jolted awake in the middle of the night Thursday by a big boom. However, police said they aren’t sure what caused the explosion. This is the second time in a week an unexplained explosion has been heard. "I heard an explosion. It sounded kind of loud and it reverberated," said a man who was jolted awake by the sound.
He thought it was coming from Longfellow Park and investigated.
"It was rather scary. I walked outside, meandered down half asleep and didn't see anything." Blocks away others heard it too.
Police took calls stretching a 14-block radius from the 3000 block of Lake Street to 44th Street. "I knew it wasn't a gunshot, so it had to be a transformer." But Xcel Energy said a transformer didn’t blow and said, "nothing in our reports indicates an explosion from our equipment." Police said they don’t believe the explosions are terroristic or connected to the upcoming Republican National Convention. While authorities aren't saying much about the two explosions, reports are calling them issues of Homeland Security.
Reports of unexplained explosions in Minneapolis actually started years ago. Residents said another explosion was heard in a 14 block area in south Minneapolis from Lake Street to 44th Street East. (video of residents discussing the startling noises)

CANADA - JULY 31, 2008 - Mystery deepens surrounding Kincardine area explosions - The mystery has deepened surrounding explosions that shook the Kincardine area last Thursday with University of Western Ontario scientists ruling out a meteor shower.
“Something pretty significant exploded south and west of Goderich and Kincardine. It could have exploded out in Lake Huron."
Highly sensitive devices installed near Lucan by Western to monitor low frequency sound waves detected a series of four impulses that lasted about a minute, starting at 11:12 p.m. on July 31. Five minutes later a low frequency rumbling was detected coming from the Kincardine area. “If you had been in London and it was really quiet outside, you should just have been able to hear the low rumble from these explosions. That’s UNUSUAL at this sort of a distance." With Ontario’s largest nuclear plant located just north of Kincardine, the explosions have triggered international media interest. Officials at Bruce Power have said there was nothing unusual at the nuclear station. South Bruce OPP were inundated with 911 calls shortly after 11 p.m. that night with residents describing walls shaking and windows rattling. The signals detected at Lucan, probably five or six minutes after the original blast, were intense.
If it had been caused by a meteor, there should have been a bright fireball in the sky. The university has a camera system at Kincardine aimed at the sky to capture the image of any meteors. “We have already looked during the time interval of interest. It was clear that night and no meteor.”
The monitoring devices at Lucan indicate all of the explosions occurred in the same area south and west of the Kincardine area and south of Goderich. In the past, the same instruments have picked up mining explosions in Wyoming in the western U.S. and the Shell refinery explosion in Sarnia. “Based on frequency content and the phenomenology of the signals, these are not consistent from what we would expect from a meteor at all."
But the signals also don’t fit another theory, that it was caused by a sonic boom from a jet. "They are not all that consistent with shockwaves you would see with supersonic aircraft.” The closest fit for the signals from the explosion, particularly the low rumbling, would be surface blasting at a mine. The only mine in the area is Sifto Salt’s underground operation at Goderich. A worker at the mine who lives nearby said he has never felt any tremor from blasting at the salt mine that stretches under the lake.

AUSTRALIA - July 27, 2008 - Sunday afternoon around sunset there were a series of loud explosive sounds heard from one end of Magnetic Island to the other and nobody seems to know what it was. "It could very clearly be heard in Horseshoe and Nelly bays (different people I spoke to) and at first sounded like distant thunder. But it continued at fairly regular intervals for at least an hour - just before sunset - if not longer." Others heard the sound but, as they reside on the West coast, assumed it was just more live firing practice by the air force on Halifax Bay. However, after making enquiries they learned there were no exercises being conducted at the that time. Calls to the Townsville Met Office, the Harbour Master and even Cluden race track (did you have a fireworks display after the races?) resulted in three big "Nos".

MYSTERY VIBRATION [perhaps related to the mystery booms? -

WISCONSIN - JULY 24, 2008 - A couple claims a mysterious noise plagues their house in Green Bay. The noise has been plaguing them for two years and sounds something like a rumbling motor, with a subtle vibration that won't quit. Then it stops - especially when they try to show city officials or acoustic experts what they're hearing. "It's like there's a semi parked right outside with the engine running, but when you look out, there isn't one." The couple have lived in the same house for 42 years. The problem only developed over the last two years.
When they leave, the don't hear the noise, so they know it's not some health problem the two share. City officials hired a company for $1,000 worth of testing in the house this spring, but the tester came up with no noise and no significant vibration. The local alderman has heard the sound. "It's like an engine thing, a low-frequency vibration. I think it would be an annoyance." The immediate neighbors haven't complained, although some people have said they heard the sound.