Thanks.

 

Siyan, that noise is the main climate control blower fan. You might have some trash in it. Open the hood and remove the dust filter (above the battery) and you can check the "squirrel cage" to see if there's anything in there. If not, then it's probably a bad bearing and the motor will need to be replaced.

 

I'll have a look tonight. Thanks. I suspect bearing though since its temperature dependent.

 

+1 that is typical. See posts by Cintoman on the W203 forum. He's in RI.