High pitched RPM related whine has me guessing

Maintenance/Repairs
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1

A question for the pros,

I have a 99 Accord, automatic trans with over 197,000 miles, appropriately maintained.

What is the most likely cause of a very high pitched whine that comes up when throttle is being added? Here’s some facts:
-This is not a constant, or even a daily occurrence. Very randomized. I think I first noticed it over a year and a half ago (20,000 miles).
-The sound will continue if the transmission is put in neutral and the RPM maintained (usually 2,000 - 2,500).
-If the A/C is on when the sound happens, it will go away when I turn the A/C off.
-When the sound is happening, there are no adverse symptoms to go with it. The car runs and drives quite well.

I have a mechanic that I patronize, so you may ask why I don’t simply have him go for a test drive with me? Well, this issue is just that inconsistent. It may give me hell all day on a given day, and then not make a peep until the following week.

Accordion

2

I had the same symptoms, except the AC part, on my '88 Accord.
It was a faint whine and never got worse, so I let it go.
Turned out it was the water pump.
Went away when I had the timing belt and water pump changed.

3

Maybe a bearing in one of the pulleys getting old. Since you say it goes away when you turn the AC off, the compressor would be the first suspect.
It probably isn’t something requiring immediate attention. The car could be perfectly fine but since you are curious, you could get a cheap automotive stethoscope (harbor freight, autozone, etc - $10) and probe around to make sure.

4

Thanks and thanks!