I can't help with the grenade/flash bang issue, but whenever I search for games and end up by myself waiting for others to join for minutes on end it has something to do with my internet. Check to see if your internet speeds are correct. Run speed tests multiple times to confirm the results. Also run tests for dropped packets.
In regards to you not being able to find a match, can you let me know if you are running from a wired or wireless? Have you properly set up port forwarding on your router?
Check out this article describing the process: Activision Support
Now, with your grenades/flash bangs, is this occurring every single time you throw the piece of equipment? Can you try clearing the console cache, and see if that helps at all?
How to clear Xbox Cache: How to Clear Xbox 360 System Cache | Xbox Support - Xbox.com - Xbox.com