Sounds pretty good to me, on my bike all you hear at idle to about 2 grand is the clanking and banging of the engine output shaft anti-backlash gear. I drowns out the exhaust note!
Check the clutch cable adjustment with the engine off. Pull in the clutch and let the lever snap back. Listen for the arm at the lower end to hit the muffler with a clank. If it does, adjust the cable so it doesn't, and then do the bolt and nut adjust to get everything else the way it should be. I had this on my bike and it took a couple months before I found it. The 75mm spec for the cable is about 3-4mm too long for some K75's for some reason. I am not the only one who had that noise.
If it really bothers you, pull the drive shaft, lube the splines, and check the universal joint at the front end for slop or notchiness. Then you'll know that everything is cool back there.