1998 Civc DX with automatic transmission and around 179,200 miles.

The other morning, I noticed a whiring/whining noise when accelerating. I could hear it over my AEM air intake and Flowmaster exhaust so it was fairly loud. The noise would rise and fall with the RPMS. The car seemed to be running fine. The idle was good and I pulled it hard in both third and fourth gears and everything seemed okay. Now, the noise isn't there all the time, but its still there.

I've been getting consistently between 31-33 MPG in the city since April. I got gas a couple of days after it started making the noise and I only got 27MPG. Same route, same driving style, same weather conditions, etc. What's going on?