Motorcycle Repair: Strange Noises?, clutch lever, cam chain

Question
Hello,
I just bought my first bike about 3 days ago and it seems to be in very good condition.  It starts, idles, and drives well, but it is making a few sounds that leave me scratching my head.  I order a factory service manual, but it's not here yet so here are my questions:

-What is the constant metal on metal sound coming from the front of my engine?  Could it be the cam chain?  Does my bike (1979 Yamaha XS400) have an adjustable tensioner for the cam chain or do I have to replace it?  How difficult is it to replace?

-Anytime I am moving and squeeze the clutch lever, I hear/feel a constant and steady clunking in the front of the engine.  This is only when I am off the throttle and coasting with the clutch lever squeezed.  It seems to slow down as the bike slows down.  What could that be?

-My bike starts on first try with the electric start or the kick.  When first started it idles at the textbook 1200rpm, but tonight I noticed that when the bike was been driven for awhile (when it's warm) it idles much higher (1600-1800).  Is this normal?  Should I try adjusting my idle?  If I lower my idle would my cold idle be too slow to keep the bike running?

THANK YOU for any help you can give me.  

Answer
Here we go! lol  1st of all the noise is normal, as long as it's not excessive.  There should b an adjuster, but please wait on your manual as these procedures r easy to do, but complicated 2 explain.

Second "clunking" noise forces me 2 ask u this, How many miles r on the bike?

Your idle issue sounds like timing, or dirty carbs.  It also makes me ask this, Is it getting colder 50-70 at night where u r?  Colder means leaner air/gas mixing and this will jump your idle.  After the bikes sits at idle for a minute or so this idle issue should correct it's self with a quick crack of the throttle, only if cold is the issue though.