Turbo Boost Noises (200Q)

[Michael Callaghan <mikecallaghan@yahoo.com>]

This may be related to another problem I've seen discussed here. If
so, please forgive me. 

I have a noise (who doesn't?).

At first I thought it was something in the suspension. It seemed to
happen only during shifts from a lower to a higher gear. It sounds
like muffled machine-gun fire. Or, for the non-violent types, it
sounds as though someone is doing a quick drumroll on my floorboard
with two rubber malletts.

Anyway, I've narrowed it down to this: the sound only occurs AFTER any
amount of turbo boost (1.0 or higher) on the boost gauge. It occurs
only when the boost drops off quickly (e.g., I let off the gas to
shift). If I ease off the gas pedal slowly and let the boost drop
below 1.0, then shift, the noise does not appear. 

The sound apparently originates from the area near the ECU. I have not
yet determined its exact location.

Does anyone know where to check from here? Please don't tell me to buy
the manuals. I'm working on that already (thanks).

MikeC
'90 200Q
'98 Expedition

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