EGR valve whistling?

[manimal]

Has anyone experienced whistling noise originating at the EGR valve?

Our 96 has an ongoing high-pitched whistle (sort of sounds like a small turbo) that occurs under specific conditions that would normally coincide with the EGR valve being open.

Noise is NOT present at any speed while idling, regardless if vehicle is in park or in gear. Noise is also NOT present during light acceleration, heavy/WOT acceleration, coasting, and cruising on flat ground.

However as soon as you are at light/mid throttle and encounter a slight grade or load condition, the whistling begins. If you reduce or increase throttle, it will change pitch or go away, depending on how much/little you give. If the transmission downshifts (shifting to lower gear = lower engine load) it will generally go away immediately. Almost sounds like it could be a vacuum leak, but the engine shows no telltale signs of vacuum leak.

I have never had an EGR code, although the DPFE has thrown a code twice, both times the DPFE was replaced and immediately the code was eliminated. Probably last time that happened was 10 years ago.

I suppose I could just unplug the EGR vacuum solenoid to try forcing the valve closed, then run a few test trips, but this too would throw a code and may affect some other issue that even if unrelated, could contribute to this whistle.

Can carbon buildup in the EGR valve cause such an issue?

Is it perhaps just the exact position/range of the throttle plate causing this whistle?

 

[Runnin'OnEmpty]

There's a filter-like gizmo on the side of the IAC valve,
that sometimes makes a whistling sound. You might
check that out. I suppose an EGR valve could do that
if it was getting clogged...?

 

[manimal]

Already removed and cleaned the IAC filter and as far as I know the IAC is not in play when driving at mid throttle.