My '98 LX has been undergoing some rough idle, not sure why and I don't want to bring it to the shop just yet because it doesn't happen all the time, only sometimes while driving the car's idling is normal, around 700rpm.

Sometimes while the car's idling, the inside shakes, I can feel the rattle of some of the interior pieces, (coins in the drink holder). I'd like to get an idea of what the problem is before bringing it to the shop, so I can kind of narrow it down before telling the mechanic what the problem is exactly.

could it be the belts?