Mechanic replaced Serpentine Belt on 2004 Honda CRV. I immediately noticed a whining sound emitting from front right engine compartment. Has progressed from whining to sound of airplane taking off or wheels being lowered for landing - all over 3 month period. Mechanic replaced alternator - still has whine. Another mechanic replaced tensioner pulley and bearing - still has whine. Yet another mechanic replaced the power steering pump - still has whine. Another said it could be the A/C clutch - when you turn on A/C the high pitch sound lessens but is still there. I am at my wits end and out of money. The sound is the same when in park and driving down the road. It never goes away. When I let off gas going downhill sound is still there. Please help.
If this noise is coming from a belt related component, I don’t understand why a stethoscope didn’t find the source. But I do understand that the tensioner pulley on this vehicle is really sensitive. With the belt on, you should see alignment marks on the tensioner pulley assembly. They should line up. The mark shouldn’t wobble back and forth with the engine running either. If it wobbles or the marks do not line up, you have a bad belt or a bad tensioner. To test the tensioner you will probably need to remove the tensioner and put it in a vise in a careful and safe position. Then using a torque wrench and see how many ft. Lbs. It takes to get the mark in range. It should be 19.5 to 26.8 ft lbs. 
Thank you for responding. 2nd & 3rd mechanics did use a stethoscope and were sure they had found the source of the problem. When the whining was still present after “repair” they stated sound could originate from elsewhere and travel to various parts? I am a female and know nothing about cars. I will take this information to a different mechanic and see they are willing to give it a try. I will provide update.