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Engine noise in hot weather

During hot weather periods my '98 Ford Ranger makes an annoying engine noise when idling, which generally goes away upon increased engine RPMs - but as the outside temperature persists, the noise remains. It appears to come form the right front away of the engine. This phenomenum does not correlate with increased engine temperature, there is no problem starting the engine during these events, and the engine does not stall - all things appear normal excpet for the engine noise. I had a new theremostat installed about 18 months ago, but this seems uncorrelated as well. Any thoughts or comments would be appreciated!

Can you describe the noise?
Is it repetitive? Changes with engine speed?

Does the A/C have to be ‘on’ for this noise to appear?

It is a loud humming noise, which does not change in frequency, pitch, or intensity, except upon acceleration (increased engine speed), when the noise goes away. The hotter the outside temperature, and perhaps engine temperature (which may only slightly increase), a higher rpm (engine speed) is required for it to go away. On one of our hotter days (105 F), the noise would not go away even at higher engine speeds. This noise occurs even if the A/C is not even turned on, and will persist if I turn on the A/C after the noise begins.

No, the noise appears regardless of whether the A/C has been off all the time or if I have the A/C already turned on. And if the A/C has not been on and the noise begins, the noise persists after I turn the A/C on.

can you video tape the problem and share it here .

Another 7 year thread opened…