Belt slippage at start when cold on 1996 Isuzu Rodeo

One of the belts are slipping on cold starts (overnight when the engine is cold in winter and summer) but not every day. Don't know which one but feel it has something with the the vapor recirculating pump. The slipping lasts 5-10 seconds and stops. Belts are tight and also tried dressing.

Asked by for the 1996 Isuzu Rodeo
The belt isn't slipping- a belt driven accessory is starting to lock up (not turn like its supposed to) and the serp belt is dragging across it until it starts to move again.
A shop will need to remove the belt and check the accessories when the engine is cold to determine which one is failing.
1 more answer
Sometimes, believe it or not, a low battery can cause the alternator to overwork upon start up. The belt noise could be the belt slipping on the alternator.