Weird "rattle" coming from engine after -5c winter ride CR 125

[twitchxxx]

So a few weeks ago I took my '99 CR 125 out on the lake in about -5c temp(without doing any jetting changes) and rode around for about half an hour, I only cracked on it a few times and didn't hold it for more than a couple seconds. About half way through my ride I noticed a weird "rattling" sound that sounded like it was coming from somewhere inside the engine. The rattle would change with the rpms as well and sometimes go away. I checked my coolent pump, pinion lever and vales and they all looked fine. Anyone have any ideas of what it could be?? Engine still has 155psi comp cold.

[MysticMotorsports]

partial piston seizure... take that cylinder off and see what that piston looks like.
if it just got the skirts then it will still have ok compression but will have piston rattle due to excessive clearance.

[DStad]

i have the exact bike. even after i rebuilt it i had the exact noise. ive been told that it could be a wristpin or mabey the powervalve set up is not adjusted properly. my rattel goes away after my bike warms up. u got any pics and mods that u want to share. i bought mine for 800.00 all orginal all the way down to the chainadjsutments and trans oil. the guy i bought it from sold it so cheap beccacuse his kid hurt it self