Skoda Octavia 2006 1.9 TDi Strange Sound From Engine Bay

Hi.
I wonder if anyone can advise me on a problem that's occurred to my motor 1.9 TDi Octavia 2006, over the last couple of days engine is idling perfect, no knocking or erratic from the engine and sounds sweet, but if you rev the car to about 1800 rpm, get a strange and very loud sort of rasping/resonating from the left hand sound of engine bay, around the EGR, boost pipe, timing belt casing area, been under car today to check for exhaust leaks and boost pipe leaks ect, everything is seated nice and not even a bit of weeping around the boost pipes, cant find visually or by feel any exhaust leakage, felt around the EGR cooler for leaking all seems well there, got a friend to block exhaust at tail pipes whilst I was under hoping to find a blow, there doesn't seem to be any leakage no fault codes, minimal loss of performance, fuel consumption is as expected, no oil excessive loss/leaks, no water loss or leaks, car boosting normally and no oils misting at all around the turbo area also, no smoke at all, really not sure how to move forward now to find the issue and what and how to check next.
Any advice would be greatly appreciated.