The windows roll up/down slowly and/or chatter!

Clean out the rubber window channels of any debris (including the felt wipers at the bottom) and then wipe down the insides of the channels with baby powder. Clean off the visible/outsides with a damp sponge.

Should help in most cases, and certainly help prolong the life of your weatherstripping. Won't hurt the window regulators, either... They're notoriously sensitive to debris in the channels.

You could also use graphite, which is a little less visible since it's black... But it is *really* messy and can get onto stuff (interior, clothing, etc.). The baby powder is barely visible anyway, and no harm if it gets onto something.

Do NOT use silicone. While it's good for the rubber, it'll make your windows stick/chatter even more and leave a nice goo on your glass.