Probable electrical problem

Hello all, I drive a 1999 Tahoe (5.7L gas engine). I believe it has an electrical problem somewhere. When I drive it, there is a subtle but audible high-pitched whistling sound from the engine that changes in pitch with respect to the engine's rpms. It almost sounds like a turbocharger on a diesel engine. In addition, if it's at night and the lights are on, the clock display / dash lights flicker slightly. The whistling doesn't seem to exist all the time, and the lights won't flicker when it doesn't whistle.

What are the possible causes for this? I have replaced the alternator, but that didn't fix anything.

Thanks,
TG

Sounds like the alt. I know you replaced it, but 2 things to look at.
1. What is the condition of the battery and cables? if the battery is low or there are corroded/ loose cables , the alt will have to work harder.
2. Maybe you have a bad alt....every once in a while a new part can fail

I agree with Merlin. Make sure you get a GM part. I tried Napa stuff for alt and I'm on my 5th one on for my Grand Am. You will pay a little more but its worth it. My Surb was doing the same thing as your tahoe.