Hyundai Repair: Sonata engine noise after timing belt change, timing belt replacement, frequent causes

Question
I just had the timing belt and water pump changed in my 1995 Sonata, which has an engine from the 1999 year Sonatas.  I'm in Australia (I know the topic is for the US but I'm hoping that they are not too different).  The engine is a 2.0L - if the US Sonata doesn't have that size it's the same engine as in the Elantra.  Straight after the work the engine is now much louder than it was.  It sounds like one of those boy-racer type exhausts except the noise comes from the engine not the tail pipe.  What could be the cause of this?  Could the timing belt be fitted wrong, or could the shop have fitted the wrong timing belt (that is, the 1995 one instead of 1999)?

Answer
There are two reasonably frequent causes of this noise I can think of that occur after timing belt replacement:

1.  Your front exhaust pipe is now leaking.  This can occur because the flexible portion of the pipe was stretched and compressed when raising and lowering the engine to facilitate replacing the timing belt.

2.  The timing belt is not tensioned properly, causing it to flap up against the timing belt cover.  If this is the cause of the noise, DO NOT RUN THE ENGINE!  The timing belt could jump time and cause extensive engine damage.