AGR Cooler Noise: Interesting Phenomenon in TDI Engines

Friends,

I've made an interesting observation regarding the noise behavior of the EGR system.

As mentioned in the technical articles, a broken flexible pipe connection in the EGR system can often cause noises that resemble those of a worn-out bearing, or even worse, make you think of a faulty turbocharger.

I've now found a completely different part that's causing those noises:

The bypass valve of the EGR cooler. This valve is actuated depending on the EGR demand, either by a vacuum actuator or an electric actuator, to direct the exhaust gas through the cooler or, as in the "warm-up phase," to route it around the cooler (bypass).

Recently, I was quite sure I had a bearing failure somewhere in the rotating assembly, as the resulting noise was perfectly reproducible (frequency-dependent on speed, from 1500 to approximately 2500 RPM). However, it turned out that the bypass valve was causing the problem.

As a test, when the engine was warm, I briefly disconnected the vacuum hose to the actuator and that solved the problem!
The suspicious hose with the flexible section is actually located BEFORE the radiator (between the exhaust manifold and the radiator), and it's in good condition, as is the one that comes after it.

It's hard to say whether this is a constructive issue or just a "trivial problem," but I think it's also something that people with different engine codes might be losing sleep over because of similar issues.