Random Intermittent Exhaust Noise. Wtf?

[jjman]

Iv got a bit of a random sound problem that I thought id see if anybody could shed light on, or perhaps may have experienced...

Basically my car has started making a random, intermittent sound that sounds like it is coming out the exhaust.

it is like a half to three-quarters of a second sound that is like a loud 'whooomp' or 'borrrr'.

It doesn't seem to affect power at all.

It happens anywhere between 3000- 4500 rpm n usually under a half to 3/4 throttle going up through those revs. Can also sometimes do it on full throttle.

Bottom line is that I have an assortment of small holes developing in my mild-steel cat back exhaust section, including one in the centre resonator.
I am assuming that somehow the unburnt fuel is being reignited into the exhaust from the holes (or out of the holes). The car has an aftermarket turbo n all the tune n fruit to go with that. Otherwise a 3inch turbo back exhaust with 200cell cat (which probably doesn't burn all the unburnt fuel being 200cell on a tuned car).

Is that aforementioned scenario likely or even been experienced before by someone? or is there perhaps something more sinister going on like a failing VCT,CAS or tune out etc??

cheers

J