Had this problem .
I've rescued a few Hoovers and Eureka's from the same era,70's-90's that rattled so loud you could barely hear the motor. Here's what I found to be the common reason(s) on all of them. The end caps wouldn't seat properly due to excessive wear on the ends, the little oval or square that pops in to hold the roller in place was chewed up or rounded. On one roller the ends had been screwed to tight and this reduced the width of the roller to the point that I couldn't get the roller to reach both sides of the nozzle. So I loosened one of the round roller ends a little until I had just enough width to fit the roller down into the holders.
There are felt lined 2-piece holders or dampeners that cradle the roller when the nozzle plate is fastened. Some models have one others up to three. The felt wears down and can usually be replaced. If your lucky, the felt can be pulled up a bit with needle point pliers or tweezers and you can get a little more use from them.
I was able to re-grease the roller bearings in a couple which helped with the noise also. Flip it over and remove the bottom plate and run the machine to see if you can isolate where the rattling is coming from. Most people would order a new roller, I just didn't want to spend 25.00 on a cleaner I wasn't sure I was going to keep. Hope this helps in some way! Billy