TDI Engine gets loud at 2100 RPM

I took a chance and bought a '96 Passat TDI Wgn with 12200 miles on it in Aug. of 1999.
We know have 134000 mi. on it and it's been a great car.

At 2100-2200 RPM the engine gets louder but as you get over 2200 RPM it quiets down again. I had a 1984 Jetta Turbo Diesel and seem to remember it doing the same thing. But it was loud most of the time.

My father has a '98 Jetta TDI and I can here it on his but it doesn't seem to be as loud.
Has anyone else noticed this? I've thought it's just a normal resonant frequency but it's bothering me and I'm wondering if I can do anything about it.

The Passat TDI is well known for this, they all do it ... until you replace the exhaust system with something different.

I now have a custom-bent stainless-steel cat-back exhaust system on my car. The 1200 and 2400 rpm resonances are gone, replaced with a slight resonance at 1600 rpm. I do more highway driving than city driving, so this was a worthwhile tradeoff.

Any muffler shop that advertises "custom mandrel-bent pipes" or similar can do it. Insist on a low-restriction-type muffler ... they may advise against it, but do it anyway, it won't be too loud.

The Techtonics aftermarket exhaust for this particular car isn't stainless steel, at least the last time I checked. Only stainless steel will stand up to the road salt they use here!

Brian P.
'96 Passat TDI

My 1996 Passat still does the harmonic oscilation at around 2200 rpm. I can see the mid muffler shaking when someone else revs and holds the engine at that speed while the car is stationary. Pushing against the exhaust to dampen the motion makes the noise stop completely. Now that the exhaust has over 135,000 miles and some of the metal has rusted off, the natural harmonic period has changed slightly and the noise is less noticable. Either that or the noise has caused a hearing loss.

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3.5 liter Passat
"Lupo? I don't need no stinking Lupo!"

My car ('96 wagon) doesn't do this at all, but my brother's car ('96 sedan) does it a lot at idle, and again at (I think) 2500rpm.

I can see his whole exaust system vibrating, and if I grab it it stops.

I guess I just have to thank my lucky stars that my '96 hasn't ever done it!

Mark