Toyota hilux sr5 exhaust leak - HELP

I have an exhaust leak that i can not find - here is the scenario and what i have to locate it so far --

Exhaust leak can only be heard when motor is under load , ie you will not hear it when idoling, rev whilst in neutral - no exhaust leak evedent - hit the road and its instantly there - it almost sounds like an individual cylinder leak as its not a contant leak sound but every 6th fire ( if you know what i mean ?)

now - whilst i had a friend block the exhaust with his foot to allow pressure to build in the exhaust system - i got a spray bottle and sprayed around every where there are gaskets and a point of a possible leak ( with soapy water ) --- found a very small leak between the cat and the header pipe -- so fixed that ( but not the problem )

One of my customers ( chatswood toyota ) suggested it may be the power valve that goes from the exhaust to the intake manifold - the noise does sound like its comming from drivers side of car - i can not see any evidence of leak - tried to put the car in gear and load up with hand break on , but can not get same results as ON road

has anyone else had this problem before ??? can anyone suggest anyting to me ????

Car is a 93 Toyota Hilux waggon - 3 Litre v6 SR5

thanks

Frank

sydney Pumps