This is a warm engine by the way, it doesn't make this noise when cold.
Classic camshaft endplay knocking. Nothing to worry about.
Excessive camshaft end play knocks only at idle, only when hot, and stops knocking if idle is picked up to a fast idle speed close to 2k rpm. I had the camshaft end play knock in both my GSs in the past and although I haven't heard it in mine for years now this one just doesn't sound like it to me, frequency is all wrong. Perhaps checking it with the leaning to the left test suggested by Suzuki in their service bulletin would confirm it? I have a copy of it that's hard to read, best I could find:
http://img.photobucket.com/albums/v443/jcp8832/CamFix_zps454a0fb8.jpg
I first listened to this one before bombsquad83 posted and thought it sounded like the loose starter clutch rattle but volume is too low for me to be sure and OP stated it didn't knock when cold. I had the starter clutch knock (rattle) earlier this year and it does knock hot or cold at idle up to 2-3k rpm so I was waiting to hear other opinions on it. Doesn't seem like either to me now and there are other possibilities unless lean test confirms camshaft knock. :dunno_black: