whyjay91

Hey gang, I've got a B7 2.0T with 60k miles and it has been sitting for a while in the garage. I fire it up every month or so and sometimes drive it a few miles. It recently developed a rhythmic thumping sound that is most audible near the airbox. I looked it up and many point to the camshaft, some throttle body, and a few other components. Odd thing is that once I let it warm up a little, as soon as I tap the accelerator from idle, the thumping noise is gone. I removed the airbox, checked the freshly changed oil level and don’t see any issues. Oil, coolant, and other levels look great. Drives completely fine. It will make a light thumping sound from the engine compartment/airbox all day long until I give it a little gas. Then it is gone. No codes, no stress, no nothing.

One more piece of data is that when I squeeze the large hose to a small inter cooler on the driver’s side, it disrupts the thumping rhythm (doesn’t make it go away). Might be a red herring. Just a little rev of the gas makes it disappear altogether.

Would love to hear a few opinions from you Audi experts. Thank you!

Hayabusafalcon

2006 B7 A4 2.0T quattro 192k miles, third owner.
Whyj: I don't know what is making that sound exactly but I had a weird "air-rush" sound coming from the airbox area and it drove me nuts. The cause....anybody? anybody? class? class?
The Helmholtz resonator....
What?
Yes, the Helmholtz resonator.
The airbox actually has two inlets. Take a look at yours with the filter out. The obvious inlet duct from the front of the car, and a second that originates from inside the right front fender! True.
That is part of the Helmholtz resonator. Really. I'm not making this up. Look it up on the web. The Helmholtz resonator is a sound "attenuating" device. (Gawd! Audi (over) engineering!)
Anyway, we had the car fixed after the Mrs. hit a deer. The fender was replaced. Then we started noticing the "whoosh" sound upon light throttle while pulling away from a stop. It would disappear at speed. Hmm?
It took me literally 6-months to diagnose and cure the annoying air rush. The duct in question passes through the inner fender wall and makes a right angle to a flexible paper "slinky-like" tube which terminates with an open end between the fender and fender liner. (I swear I am not making this up.)
The cure? I simply blocked the duct with a piece of closed-cell foam sheet 1/4 inch thick by 3x 3 inches (neoprene). Cost: one dollar.
Maybe your thumping sound is coming from the same device. I don't know. Maybe that slinky tube is bouncing around?
BTW- blocking that fender duct has no ill effects that I have noticed. That was nearly two years ago that I did that.
Good luck, and all the best, Haya....(Post back, let us know what you find.)

whyjay91

Thanks for the response and information! This is definitely more of an engine sound that’s permeating through the air box. In my research some have referenced a gummed up valve where the air flows near the turbo. I also edited my original post as when I had squeezed the large hose on the other/driver’s side running to the small inter cooler, it disrupts the noise. Doesn’t go away but may be a red herring.

Thanks again! I appreciate the time!

Hayabusafalcon

whyj: No problem.
One other thought comes to mind regarding the rubber charge tubes....Pooled oil.
It is common to have some oil collect in the intercooler charge lines. In fact I installed drain plugs in the plastic connectors at the low points both upstream and downstream of the intercoolers. Monthly checks reveal none to a few drops upstream and 50-100 mil downstream consistently. I've never seen an abundance of pooled oil but have read accounts of copious amounts of oil collected there which can actually hydro-lock the cylinders if bad enough. I suspect this condition is very very rare. Nonetheless maybe there is enough oil to cause some restriction and thus the sound you describe. Its easy to check, just loosen and pull the rubber charge tube from the plastic connector. Have a pan ready, there will likely be at least some oil.
Good luck, Haya....

whyjay91

Hayabusa for the win!!! I disconnected the pipes going into the intercoolers at their lowest points possible and out came about a total of a half quart. Drained and fired her back up without issue. Also seems to run a little smoother although could be in my mind. But hey, no thumpety thump.

From my research, I will likely replace the PCV with the upgraded version with the softer spring to help with oil separation.

Thanks Haya!!!! Appreciate you!

Hayabusafalcon

Cool.
Just to kibitz a little more, take a look at going with a PCV delete kit. They have come way down pricewise. About $30.
I have had good operation since installing one 3+ years ago. Prior, I had nothing but grief with PCV's. Post if you have questions. Haya....
This is the one I used:

whyjay91

Thanks Haya! I also read up on an updated/improved PCV that I was thinking about swapping in. Looks fairly easy to do. Thoughts on delete vs. an updated version?

Hayabusafalcon

Whyj: Sorry, I am not familiar with the latest upgrades on PVC's. I would however recommend you stay away from aftermarket PCV's and go with genuine Audi on this part. I have seen durability issues when I tried A/M units before. Haya....