moribundman

If you still had the plenum installed, it functions also as an air intake silencer. I have never run the engine with the plenum removed, so I don't know how loud it would be. That awful sound in your video certainly makes me think that some part in the intake was resonating. Maybe the intake manifold started ringing?

odelay12v

it was quite horrible a sound .. it is talking to me much better now its clamped down.. only now my pwr steering pump is whining at me again.. wish i could just delete that too..

odelay12v

as the silicone hose was about 1/4 off the hvrs .. it wont happen again as now its clamped tight.. what a pita.. as i said earlier i learned if you can clamp it do. for starters i used the stock worm style clamp with out the holes in it so it wont cut through the hose..

VAP

it creates a leak that because of size, shape and engine RPM is capable of making TONS of noise. If the size/shape of the leak is just right it makes a whistle sound. The sound is simply a "compound noise" created by more than a single cause simultaneously. You have the rush of air as well as internal engine sounds all occuring at the same time. Ya can't have one without the other... it's the law!

A normal household 1/3-1/2HP vacuum cleaner is loud. I'm actually even more surprised that a 172HP V6 vacuum cleaner isn't any louder than it is! Your engine is an air pump. On the intake side it pulls air. On the exhaust side it puhes air. 200HP pumps are LOUD especially when uncapped or allowed to leak! When the air path is open you're hearing combustion noise (due to cam profile and valve duration & over-lap), valves slamming into the seats, pistons scraping and other reciprocal/rotational parts... same as if you were standing "inside" the intake manifold. Nothing "quiet" inside an internal combustion engine! You have a long path of steel tube, cats, resonators and mufflers to quell the positive pressure side noise but only silicone on the vacuum side between you and the "source" of those sounds. Unlike vacuum or positive pressure "sound" travels in ALL directions and not just "flow direction", ie; sound travels upstream "or" downstream of airflow. Shouldn't be surprising when those sounds escape from and can be heard thru the intake tract when a hose separates and is open to atmosphere. A hose that is "wide-open" to the combustion chambers. When that occurs you hear a small sampling of EVERYTHING occuring within an engine from air rushing into the separated hose to air moving past the throttle body butterfly plates to intake valves opening/closing and the air moving past them, pistons moving up/down as well as exhaust valves opening/closing and exhaust noise as well. It sounds like a metallic sound because the things that create the noise are metal. This stuff makes noise and LOTS of it!

Bottom line is it's just 200HP vacuum cleaner whose suction hose fell off and instead of an electric engine it has an internal combustion one. Loud yes but nothing more and shouldn't be surprising at all. As was mentioned previously in this thread is also why Audi refers to the OEM plenum as a "silencer" in both the Bentley repair manual and in ETKA.

Your intake tract's primary function is flow. But secondary to that it must also serve as a muffler/silencer on the "pull" side of things same way mufflers do on the "push" side. Take the muffler off the "intake side" of any air compressor and see how loud those are! And the hose that slipped off in your case is barely 1 foot away from all 6 combustion chambers. Bet yer *** it's LOUD! No surprise there! If it's loud everythings working as-designed. If that hose slips off and ALL you hear is a whisper-quiet gentle rush of air you should worry vigorously ;-)

odelay12v

makes total sense never thought of it as driving a 172 hp vacuum cleaner..