We have an issue with our 2008 Suburban that several shops have not be able to resolve. Any help is appreciated...

Randomly (once a week), after the vehicle is started (about 1-3 seconds), a very loud ticking noise is heard for about 5-10 seconds. It sounds like a fan spinning and hitting a screw or something. Loud, embarrassing noise. It sounds like it is coming from under the hood - sorry I can't be more specific.

Since it is very random, no mechanic can reproduce it to troubleshoot. Has anyone else had this issue before or could share some insight?

Thanks in advance!