trying to figure out what is going on with my 92 softail custom. 
the problem is, when im riding wide open, in 5th gear or the highway gear, at about 65+ mph(sustained amount of time at those speeds). all of the sudden i hear what sounds like something hitting my bike. metal on metal. the bike doesnt lose power and doesnt jump when this happens but i can feel it when it does. (if that make any sense). no leaks to be seen. no horrible noises. but my bike is almost at 49k miles. this has just started to happen recently. i was wondering if anyone could possibly shed some light on this for me.

You should check the primary chain tension although I would think it's something else. Were it the primary chain I wouldn't think it would take cruising speed to notice it. Also, you don't mention "where" you feel it. When's the last time it was serviced? When was the chain adjusted last? When was the last time you replaced the rear wheel. The engine and bike will vibrate differently at different speeds so many things could be going on. You might want to check the upper and lower belt guards. They have broken on me before. Other than that I couldn't hazard a guess without really know "what" and "where" you feel. good luck. Let us know, please. It'll help others later on.

Peace

Is it only when in 5th gear?  Try running for a bit about that same rpm in 4th and see if still happens.

But my first instinct would be to open the primary cover and have a look in there and see if the chain is out of adj, or anything else going on in there.  Plus its the easiest place to look inside!

It's not your bike but it's the same principle. You will not have a self-adjusting shoe (chain tensioner) on your bike. Still, I'd look at the upper and lower belt guards before I'd open anything. That metal to metal rattle just doesn't sound like your primary chain.  If that chain were loose you'd feel it "slapping" in the primary.  Look closely as breaks hard to see in these belt guards, especially where they fasten into the frame.

http://www.youtube.com/watch?v=hdS--4RQ63A

thanks for the help so far. i have not yet done any further inspection on it but i will tomorrow. i just serviced it a couple hundred miles ago. a complete service. just had the primary open(needed new gasket), looked clean. felt good. have not looked at the guards though, so i will.
i "feel" it underneath to my left, sounded like it could be a metal on metal slap? something hitting something?(origanally thought primary). the rear tire was just replaced at service.
just happens for far in fifth and the highway gears.

sure does sound like belt guards> Let us know

Gotta ask. Is you kickstand spring tight.

Good suggestion Lucky.  Never thought of that.

On our ride to Sturgis this year we had a noise coming out of the bike from down low. It turned out to be bad rear wheel bearings. It made a sound a lot like it was coming from the primary or the tranny. My question to you is does it only make the noise in 5th gear and riding fast. Good luck and let us know what it was.

Almost impossible to say without test riding it. Everything on the bike is metal so a metal to metal sound could be just about anywhere. Like others said I would start with the simple stuff first checking for anything external being loose. Then I would pull the primary cover just because that is an easy 20 minute job, and be sure nothing is wrong in there. Use a dental mirror to check behind the clutch and gears so you don't have to pull them.

Other than that, if you are sure it only does it in 5th gear, sounds like something in the tranny gone wrong.

I'm leaning more and more towards Lucky's suggest. Under the frame there's that rubber bumper that snaps into the frame. The kickstand rests against that. It's possible that the rubber has twisted so that the kickstand is banging against the frame. I really HOPE you let us know what you find.

Did you ever find where the noise was coming from?

lots of good suggestions hear.

Hey 92, did you ever get this figured out?