Most annoying problem

Hi
My P38 has a problem that is driving me bl**dy mad. Fitted new alternator as wasn't charging properly now working and charging fine, at the same time fitted new serpentine belt. Now every morning when you start it for the first time the belt squeals like a stuck pig, for the rest of the day its fine, no matter how many times it is started. This morning started it with the bonnet open but still could not find what is slipping, to damn noisy. Anybody got any ideas?

Tensioner weak, poor quality belt, alternator load is exceeding the belts transmission capability due to one or other.

Most likely its the altenator. When you start the car the load on the altenator is high as it has to replenish the battery from the act of cranking the engine.

Bought the alternator and belt from main stealer, as for the tensioner it took both hands to pull it back, and i'am not a little bloke, although I admit to being passed my prime. Could it still be one of the above.