If you flush the toilet and it sounds like there is some sort of jet engine in the tank, it may be a compressed air, assisted flush, type tank. These flushing mechanisms work REALLY well but some of them, like the Sloan Flushmate III/503, are problematic and a fairly serious safety issue.
There have been numerous instances of where the tanks have exploded and caused personal injury to exposed naked body parts (pretty common to have naked parts on toilets if you know what I mean).
While the tanks have been recalled, there are still a lot of them out there and I typically find several each year. If you have a building with one, you may have several.
There have been two separate recalls of the Series 503, Flushmate III toilets. The first recall in 2012 involved 2,330,660 units manufactured between October 1997 and February 2008.
The second recall in 2014 involved 351,000 units manufactured between March 2008 and June 2009---essentially adding a year and 3 months to the original recall.
Repairs according to the CPSC: Consumers should immediately stop using the recalled Flushmate III system, turn off the water supply to the unit, flush the toilet to release the internal pressure and contact the firm to request a free repair kit.
You want to look at the number circled in the picture below---it is the date code of manufacture.
The last two digits being the year. As you can see the year is within the recall period discussed above and repairs are necessary.
Charles Buell, Real Estate Inspections in Seattle
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WA State, Home Inspector Advisory Licensing Board