Near the end of a short (about 3 miles) drive on Saturday evening, my '93 944T (98k miles) started making a strange, intermittent buzzing noise. This only occurred when I revved the engine; it only lasted a second each time (i.e., revved the engine and held it at around 2-3K RPM; the noise would happen about 3 seconds after starting to rev up; would last about a second, and then quit, even if I kept the pedal down). It had an electronic "feeling" to it; it didn't sound in any way mechanical (not like something rubbing or vibrating). The best way that I can describe it is that it reminded me of the noise you hear on the radio when they test the Emergency Broadcast System, if anyone knows what that sounds like. With the engine still running, I turned off everything (lights, heater fan, radio, etc.); it continued to occur each time I revved the engine. Turned it off, ran in to do my errand, and restarted the car, but the noise did not return. And it has not returned yet. Has anyone ever experienced this before? It was such a bizarre occurrence, and I am waiting in fear for it to happen again and lead to something problematic. If it matters, I have been dealing for some time with a shuddering idle; so far I have cleaned the TB, replaced plugs, cap and rotor. I suspect the IAC valve, which I intend to replace when funds become available and the weather allows me to work outside (don't have a garage, alas). Otherwise, engine runs great. Is this potentially a failing relay, or worse? As always, any help is appreciated.
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Steve Van Steenhuyse ('95 944T, 97K)