I bought my GS500F new 2005. While it is sitting idling (1200)RPM there is a consistant metallic Tap,Tap, Tap every 20 to 25 seconds. In or out of gear clutch pulled or in neutral. I took it back to the shop where I bought it when it was still new, they didn't know what it was. Still doe's it to this day. Anyone know what it could be. I think it is getting louder. Thanks Mike

first thing i would check would be the valve clearance's...

Bit strange they didnt know what it was or wasnt able to help much or give much information?!

If it were more frequent it might be a loose tappet but every 20 to 25 seconds sounds like the infamous camshaft knock.  Does it only when hot, only at idle and if you pick up the idle speed to 2k it stops?  If so that's it and it's annoying but harmless.  Suzuki finally acknowledged it a few years ago and fixed new F bikes still on warranty with a camshaft and sideplay shim change.  Camshaft was knocking back and forth sideways from too much freeplay.  You can confirm it by checking the freeplay on you camshafts.

I had it on both my 97 and 02 GSs but haven't heard it for years now, think it stopped when I started using the 15W-40 heavy duty truck oils years ago.    I diagnosed it on my 97 and first published it here before I bought my 02 back in 03.

That sounds like what it might be. I have heard of it on older bikes, but did not expect it on a 05. The valves have been adjusted 3 times the last time I finally had to switch some shims. It has ran great with no problem for 6 years. I just wondered what the heck it was.