No I mean the 'whoooo' sound before the blowoff (1.00 to 1.02) which is caused by air moving through the pipework...maybe this is what he was hearing, but possibly louder in a single-cone kit?
Yeah, it does kinda sound like those 2 secs you described (thanks btw) but for much longer... it's over a few thousand RPM then dies off at later revs (starts at around 2.5kRPM till 4.5k @ WOT, then disappears) there was a good Volvo 850R video which did the same thing, but I can't find it.
It's a bit annoying tbh... I get all the intake and blow off sounds, had them on a few motors... but this just sounds wrong; self-destructive almost.