strange sound when accelerating hard
2001 Z-28 with an A4. no mods to the car

is this common or am i in for some trouble
Your PCV system is allowing a mist of oil into the intake. This has built up carbon inside of the engine. In turn, the engine runs lean, has hot spots, and pings slightly (my A4 does the same thing)
To check if this is the problem you have 2 options.
1) read your spark plugs (the hard way)
2) take off your intake lid, maf, and bellow. Push the throttle open (car off) and feel behind the throttle body plate. If it's oily, liquid or even just grimy (not just perfectly dry carbon). Then your pcv is misting oil. Mine was- but the oil level never dropped it was that slow. But after 40k miles- engine started to ping
Now, to fix it:
1) replace PCV valve ($4 or less)
2) engineer some way to seperate out the oil from the air (some people use filters...I used a home-made catch can to preserve system vacuum) $24
3) use GM top engine cleaner to clean out the intake, valves, and chambers (be sure to change oil after you are done with this process) $10
Oh, also not a bad idea to change your plugs after doing the top end cleaner. NGK TR55's are great, and it's not like platinums last as long as they are supposed to anyway.
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