‘89 wagon, auto trans.

I know one cannot really make a diagnosis by typing some words here , but thought I’d try it anyway.

Today for the first time, going from a stop and accelerating normally, had some strange “chirping” sounds from sort of the engine compartment but also like under the car towards the front. . It stopped after going a few feet tho. Weird.

So I tried a few things. Stopped the car, put it in neutral and revved the engine-no chirp. Put the car in gear and slightly revved the engine while holding the brakes. No chirp. Then-put the car in reverse, let go of the brakes and accelerated a bit, no chirp, BUT a slight shuddering at beginning of acceleration felt from the trans but ONLY in reverse.

It definitely did not sound like a loose fan belt, and anyway if a loose belt usually the sound would be heard when in neutral and revving the engine. I did open the hood to check the belts, but all tight. That’s about it. Thoughts?