SAP will start every time the cats are cold in order to aid the emissions.
Meaning has nothing to do with a temp outside.
if should whistle like a small vacuum cleaner. if it whistle more than that it maybe failing.
I thought the whistling sound is a sign there's something wrong with the SAP or there's a leak or blockage somewhere that's causing it(whistling). So you guys are saying a whistling SAP is normal even for a brand new SAP?