Strange noise from Audi 80 after revving engine

I wonder if anyone can help me. I have a 1990 Audi 80 1.8 that has started making occasional strange noises but only after the engine has been working hard(by this I mean climbing a very steep hill or
overtaking - it doesn't happen in normal commuting type driving). The weird thing is that the noise disappears about a minute after the engine is returned to normal revs. The noise itself is a kind of rattling, but in some ways it's not unlike the kind of popping and banging that you get in an old sports car when backing off (something to do with valve overlap, I think). I'm pretty sure that it's not that, though. The car has done 125000 miles, but has a comprehensive service history, and has recently had an oil change and a new exhaust. It also doesn't burn any oil, and runs at the correct temperature. I suspect that it might be something to do with the exhaust as it seems to emanate from that area, but I am a bit concerned that it might be somehing expensive, like the drivetrain or engine. Any ideas on this would be greatly appreciated. Thanks.
Jonathan Prestidge
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(Jonathan prestidge)

This will be the 1781 golf engine, Bosch CIS-E injection I think.
Could be a weak mixture or advanced timing causing pinging.
But popping noises on overrun mean you have an exhaust leak or lean mixture, since you've just had a new exhaust might just be a joint that needs resealing, probably seal itself after a while...
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