Hello Good Fellows!
I've been searching high and low for an answer to my issue but just can't quite pinpoint the problem. So let me describe as best I can and hopefully one of you will have ideas I have not thought of.
Vehicle: 1998 K1500 Suburban
Problem: Mechanical grinding noise behind and below the instrument cluster.
History: Had the engine replaced and started hearing this constant grinding noise after I got it back. Kind of sounded like it was coming from the Instrument Cluster area and my fuel gauge was on the blink so I thought maybe it was the cluster. When I took out the cluster, the sound went away. I thought I had it figured out. Got the replacement cluster and when I installed it, the sound came right back. No matter what I do, the sound does not go away until I shut down the engine. One thing I noticed is that if I am idling and rev the engine a little, the sound goes away for just a split second and then comes back. I thought maybe a vacuum leak causing some type of issue but I don't know of any vacuum-actuated devices in the truck that would sound like a grinding motor.
Other Info: No navigation system. I completely pulled the AC controller and disconnected it from the dash...no change, Took the cluster out and manually powered it up and the gauges activate but no noise within the cluster itself (not sure this is a good test...maybe it reacts differently when fully plugged into the dash harness). Removed radio.
Is there anything in that general area that could make that noise related to the vacuum system? When I turn the truck off, I hear the sound gradually quiet down...kinda like a motor spinning down. Vacuum may not be related at all but I have noticed in older cars sometimes a vacuum leak could cause different things to not work correctly. Maybe revving the engine increases voltage a bit and that is what quietens it down for a split second. Although keeping the engine revved up does not make the noise go away. It is only just a second when I rev real quick.
Any ideas greatly appreciated!
Thanks in advance!

 

Could be an electrical actuator that directs air flow for heat, AC, defrost. Some have at least three of these.

 

Thanks, Cusser! I don't really see an actuator in the area the noise "seems" to be coming from but I do know that one is not working because I cannot get the airflow to change from floor, front, defrost, etc. I will revisit that and see if I can find the bad actuator and see if that is where the noise is coming from.