These forks do sometimes have a mysterious noise at extreme - it could be a rubber stop at the bottom has gone (sometimes they disintegrate) or you may be low on oil ( 190cc in each leg if you just drain and replace), or around 210 -220cc if you're tearing the forks down and thus completely emptying them. The forks in my 82 R65LS were a bit noisy after I rebuilt them until I added a bit more oil - about 230cc in each leg now - with an aftermarket spring kit.
These forks are a bit shorter than the R80's, the springs are a bit shorter and they are usually put in with a spacer for a bit of "preload". Sometimes the noise is spring slap on the inside of the fork tube, particularly if you hear it at the upper part of the fork rather than lower in the slider area.
I suggest that you drain the fork oil and see how it looks. If you see black chunks of plastic or hard rubber, then the problem is likely a disintegrated rubber bumper. You will also get to see how much oil is in there (should be able to get out ~180 - 190cc). IF you get alot less, and no bits of "stuff", maybe its just low on oil. You can then decide whether to do a tear down or just flush and fill with new oil and see how it goes for a while.
A few pointer on the forks and oil refilling:
1. GO GENTLY on the drain bolts and DON'T follow the manual to torque them back up to 12 ft-lbs or you'll strip out the aluminim threads in the slider. Just snug up gently with a small wrench.
2. After you remove the top cap on each tube, there is a "plug" inside with an allen bolt. If you're just refilling with oil hopefully the allen bolt will come out to fill through that - otherwise to remove the top plug, you must push down on it against the spring to reveal a small spring clip that fits in a groove inside the fork tube that acts as the retainer for the plug.
3. If you do decide to tear down the forks, DO get new crush washers for the large allen bolts at the very bottom of the fork sliders.
