The rattling is normally the cover over the pulleys, when I had one of these drills, it always rattled.
The main thing to check is the quil.
Extend the quil as far as possible and give it a good tug in all directions and feel for any movement.
Next place something you know is round and true in the chuck and using if possible a clock check when running that it has very little runout. Some run out is inevitable. If there is excessive run out, the drill is only good for spare parts. Machine Spares sometimes have a quil when they have an old drill they are breaking up, but it will cost about the same as the drill!
When extending the quil, feel for any flat spots, or difficulty winding it down / up. If they have been abused the cog that moves us up and down gets badly worn. You can get another shaft and cog made for about £200!!
I'd want the original on off switch, and for it to be good condition.
Take the belt off the motor and give the pulleys a good tug, your looking for excessive play. If either have any movement, walk away. It will cost more to fix than the drill.
Lastly, with an engineers square check that the table when clamped in serval positions is true to a long straight bit / rod you've placed in the chuck. Check at two places 90 degrees to each other each position of the table. If it's not true, walk away. Sometimes to remove rust the drill stem that the table attaches to gets sanded and is no longer true causing the table to lean. The table can be adjusted side to side on some models (only say that because it did on mine) but it can't be adjusted front to back.
Good luck
