2009 F250 4x4 5.4 has had an engine noise since new. At first it was very faint and occurred at exactly 2500 RPM (I'm the only one who can hear it). This noise has gradually increased in volume and now comes in at 2100 RPM and stays until 2400 RPM. While it bugs the heck out of me, getting the dealer tech to even admit that the noise exists, is difficult. Basically the dealer wants a failure to happen before investigating further.

On a cold start in cold weather, it takes a few minutes operation before the noise is obvious. On a cold start in warm weather the noise is present after running the engine for a minute. Otherwise the noise is always present and is RPM specific. No unusual sounds when idling or at high RPM. No shiny flakes or bits in the oil.

As to the sound itself, it's like a rubbing / wobbling / oscillating noise from the front of the motor. It is just muted enough that it is unlikely to be an external component like a bad bearing. When the dealer tech inspected all the pulleys he found nothing wrong.

It makes me think that part of the phaser assembly has bad tolerances and orbits around at a certain RPM. Kind of like a worn out advance weight in an old distributor. I'll be taking it in for an inspection soon since the power train warranty will expire in a few months. The vehicle currently has 85,000 Km (~53,000 miles) on the odo.

Any ideas?