RATRUES

I have a strange noise coming from my 2003 Chevy Silverado Z71. Not sure, how to explain other than the noise sounds like it's coming from the front wheel assembly or near the axle. Here's the thing I've noticed this happening before months ago when I used 4 wheel drive or the parking brake. Not sure if the noise is related to either. 4 wheel drive works fine, possibly a wheel caliber getting stuck or maybe shifting in and out of 4 wheel drive after use. It's strange, I even left my truck with my mechanic for a week and told him what I heard and of course it did not behave for him as it did for me. Go figure! Anyone else had this problem on an 03 Silverado or at least any thoughts on the matter? Last time it made the noise was about 3 months ago and hasn't done it since till today. Strange I know. All I do know, it apparently doesn't affect driving it in any way. Drives fine. Maybe when I shift out of 4 wheel drive into 2 wheel drive it's not completely shifted. Don't know! Any thoughts would help!