Is there a rule to the number of holes you should see on the locking tab of the serpentine belt tensioner? Both of the holes are hidden on mine at the moment.

I recently replaced a squeaky, worn serpentine belt (2 weeks ago). I'm still hearing a slip/squeak from time to time, especially when it's wet out.

The belt appears taught with the engine on or off, but I think I remember someone saying ~If you can't see at least one of the holes on that tab, the tensioner is fully extended, therefore the belt is too big.

I'm using an OEM size belt and stock pulley.

 

The old belt may have glazed one or more of the pulleys, causing some slippage (and squealage), especially when wet. I usually clean off the pulleys with brake cleaner spray when changing belts -it will take off any glazing. Don't use belt dressing... it's a bandaid and doesn't fix the problem, just temporarily covers it up.
-s-