Shopping cart sound just above idle

My 96 auto is making a wierd noise once warmed up.
It sounds sort of like how a shopping carts rolling on the road 2 blocks away sounds.
IT only does this right around 1000-1200 rpms when I slightly raise the idle, and only when warmed up. I notice it at stops if I raise idle and when I pull in at home or take off from a stop just for a sec till higher rpms stop it. Twice now I 've stopped and gotten a friend to listen only to not be able to recreate it.

I'm at a loss.......

Shopping cart sound, new one on me. I'd have a hard time hearing a shopping cart I am pushing, LOL.

Try a stethoscope or cheap screwdriver version to isolate the sound. Does it in Park also?

Edit: on a ride along my wife says it sounds like an soft "airy, whirring" sound

It's been dry here the last few days and I can't get the sound to come back.

I'd suspect the idler pulleys or something in the belt drive


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Well I had a friend and XJ owner come over and I apparently had my belt about 15 ratchet turns too tight. Hoping now that tension is correct I haven't thrashed a bearing now.
Hopefully the noise goes away