'99 Camry noise

I have a '99 Toyota Camry that’s recently started making a strange noise that sounds like it’s coming from the front end/engine compartment.

It’s a intermittant moaning sound that starts after the car has been warmed-up. It doesn’t happen at any certain speed. Whenever I let off of the gas or speed up it stops.

I had the car checked out by a mechanic friend, he’s checked out the brakes and the front end and says he doesn’t have a clue.

I’m stumped and my only means of income is my disability check, so taking it to the dealer isn’t an option.

Any suggestions???

Any help would be greatly appreciated!